DACS_AUTH_TRANSFER(8) DACS Web Services Manual DACS_AUTH_TRANSFER(8)
NAME
dacs_auth_transfer - transfer credentials between federations
SYNOPSIS
dacs_auth_transfer [dacsoptions[1]]
DESCRIPTION
This web service is part of the DACS suite.
The dacs_auth_transfer service securely exports credentials (which represent an identity) from one DACS federation to another (or from DACS
to a different identity management system), or securely imports an identity from one DACS federation to another (or from a different
identity management system to DACS). This ability to transfer credentials (i.e., import or export them) lets a DACS federation federate
with another system, creating a "super federation" with single sign-on capability. DACS calls such federations affiliated federations.
A DACS federation can use dacs_auth_transfer to leverage authentication mechanisms not available to it, other systems can use it to
leverage DACS, and users can potentially access any access-controlled resource located in any of the cooperating federations.
In a Nutshell
For two DACS federations, here is how the service is typically used. A user authenticates somewhere in Federation A, obtaining
credentials understood only in that federation. One or more jurisdictions in Federation A will provide a link labelled "Transfer Login
To Federation B" (or similar). Alternatively, or additionally, one or more jurisdictions in Federation B may provide a link labelled
"Transfer Login From Federation A". Later, when the user decides to access resources in Federation B, he follows one of the links.
Assuming all access control constraints are satisfied, new credentials will be returned to him that are understood in Federation B. His
existing Federation A credentials continue to exist.
The user is now recognized by both federations. If the user is known as FedA::J1:bobo in Federation A, then he will also be known by
that name in Federation B. If Federation B happens to have a jurisdiction named J1 and a user at that jurisdiction named bobo, that
user (FedB::J1:bobo) is separate and distinct as far as DACS is concerned.
Note that, in general, it is not correct in the scenario above for Federation B to automatically initiate a credential transfer if an
unauthenticated user (with respect to Federation B) is denied access. This is because Federation B cannot tell with which federation it
should be initiated (if there is more than one) or even if this is something that the user wants done (perhaps the user needs to
authenticate in the usual way at Federation A). Therefore, except perhaps in special circumstances, explicit user interaction is
necessary.
For DACS, the complete protocol is implemented by one program, dacs_auth_transfer. It provides the importing, exporting, and
server-to-server stages of the protocol and it can also optionally assist middleware with the initial presentation stage of the protocol.
The protocol is described below.
If an identity needs to be imported to a non-DACS system, that system must implement the identity transfer protocol described here, or a
subset of it. If a non-DACS only needs to export an identity to a DACS federation, it may only need a small amount of middleware to
initiate the transfer.
Security
1. A small degree of cooperation is required between DACS administrators at two affiliated federations so that they each know how to
configure the feature. The two federations remain autonomous, however.
2. Transferring credentials to a DACS federation neither creates a new account nor creates a new identity. It merely converts
credentials that were obtained in one federation into DACS credentials that are recognized within another federation. Because a
DACS user identity includes a federation name, among federated DACS systems a user's identity is unique. After transfer to a
different federation, the original credentials continue to exist and are unaltered.
3. Exporting credentials to another federation and later transferring them back to the initial DACS federation (or exporting
credentials within a federation) will replace the initial credentials with new ones for the same identity. The two sets of
credentials will not be identical, however, and the imported ones may be less complete and therefore "weaker" than the original
credentials with respect to authorization processing.
4. System administrators should ensure that dacs_auth_transfer is configured so that it is impossible to import credentials to a
federation from which they were exported, otherwise it may be possible for users to defeat the expiry of credentials by repeatedly
regenerating them.
5. The identity transfer protocol includes a server-to-server operation that must use SSL. The identity of the server issuing the
request must be verified, either through its X.509 (SSL) client certificate, DACS credentials, or perhaps its IP address.
6. As an additional security measure, a jurisdiction will only accept credentials for an identity outside of its federation if enabled
by ACCEPT_ALIEN_CREDENTIALS[2].
7. While this document talks in terms of a DACS federation importing credentials, importation actually takes place at a DACS
jurisdiction, just as authentication does. That target jurisdiction is similarly responsible for the resulting credentials and is
identified within the new credentials for access control testing and audit purposes.
8. Any appropriately configured jurisdiction is capable of exporting or importing credentials. Some federations might choose to create
"administrative jurisdictions" solely for this purpose (e.g., export.example.com and import.example.com), however, just as a
federation might be structured to limit authentication services to a designated jurisdiction.
The Identity Transfer Protocol
Overview
The ability to transfer credentials from one identity management system to another is a feature that can be beneficial to both users
and system administrators. For users, it can provide the convenience of single sign-on; a user need only be authenticated by one
federation to be able to access resources within a different federated system. For a system administrator, it means that fewer user
identities need to be created and managed.
The systems being federated might exist within a single organization or be associated with different, autonomous organizations that
have a trust relationship, very much as DACS jurisdictions do. The transfer of credentials need not be reciprocal; that is, Federation
A may allow identities to be imported from Federation B but not vice versa.
The architecture of the transfer mechanism is primarily constrained by the typical browser-oriented usage of DACS, where credentials
are encapsulated within an HTTP cookie, thereby dictating how credentials are set in an off-the-shelf browser and when credentials will
be sent by the browser. The approach is complicated somewhat because a DACS user may have multiple concurrent credentials or may be
unauthenticated. Also, a DACS federation may wish to federate with more than one foreign federation. Therefore, interaction with the
user will sometimes be necessary so that she can select the particular identity to be transferred and a target federation to which that
identity is to be transferred. A jurisdiction or federation must be able to customize this interaction for appropriate web site
integration (i.e., look and feel), but a bare-bones capability must still be provided by dacs_auth_transfer.
The design tries to balance security, usability, performance, availability, configuration complexity, implementation effort,
administrative needs, generality, and extensibility, all within the constraints of the DACS architecture and requirements.
Though it is assumed that SSL is used to secure all network communication and identify the communicating hosts where necessary, some
major potential threats against a transfer capability must be addressed by the design:
1. Replay: the system must prevent the malicious or accidental use of expired credentials, reuse of authentication material by a
different browser user (such as through browser history or a bookmark), use of authentication material discovered in a log file,
and so on
2. Forgery and Tampering: the system must prevent a malicious user from changing authentication material to get different or "better"
credentials using the transfer protocol
Replay is addressed in the transfer protocol by restricting the exposure of authentication and protocol material and by limiting its
validity period. Injection of copied material is also made difficult. Forgery and tampering are addressed through cryptographic means;
using well-established techniques, it is thought to be practically impossible to create forged authentication material or modify it
undetectably.
Security
Importation of identities has federation-wide ramifications but it is the responsibility of each jurisdiction to decide whether it
will allow its dacs_auth_transfer service to import an identity or its rules to honour an identity imported by another jurisdiction
within the federation. A jurisdiction may independently allow identities to be imported from an external system, just as it may
unilaterally decide whether it will authenticate users and how it will do so. On the other hand, a jurisdiction is free to reject
imported identities, just as it is free to reject an identity vouched for by another jurisdiction in its federation. Federation
members may wish to establish guidelines and procedures for importing identities.
Protocol Operation
The purpose of the protocol is to transfer an identity understood by the initial federation to the target federation. The initial
federation exports an identity; the target federation imports the identity.
The four stages (operations) of the protocol are now described, in the order in which they are used. In all cases, "the user" can be a
browser or middleware.
1. The PRESENTATION operation, which is performed in the initial federation and is optional, is used for prompting the user to select
the credentials to be transferred and identify the target federation. The purpose of the PRESENTATION operation is simply to make
it easier for a user or middleware to invoke the EXPORT operation; the EXPORT operation can be invoked directly without engaging in
this step of the protocol, however.
2. The EXPORT operation is invoked at the initial federation by a user to request that the initial federation initiate the transfer of
credentials representing a given identity to a given federation. After receiving and validating its arguments, the EXPORT operation
invokes the TOKEN operation at the target federation. If the target federation tentatively approves the importation of the
identity, it returns a URL to which the EXPORT stage redirects the user. If the target federation rejects the request (or the
request fails), the EXPORT stage returns an error indication that should be reflected back to the user and terminates the protocol.
3. The TOKEN operation is the heart of the protocol. By invoking it at the target federation, the initial federation vouches for the
identity to be transferred and requests that the target federation honour the user's request for credentials valid within the
target federation; the latter is free to reject the request for any reason. To accomplish the transfer, the initial federation
requests a token from the target federation.
A token is cryptographically protected, opaque information encapsulated within a URL as its query component; the token is
meaningful only to the target federation (i.e., its meaning is unspecified by the protocol). It could contain a database key for
the transaction, a nonce, or a self-contained description of the transaction. All that is required by the protocol is that it be
kept secret among the communicating parties for as long as it is valid, that its validity period be no longer than what is required
to complete the last stage of identity transfer, that it be difficult to forge, and that it be tamper-resistant.
If the request for a token is granted, the target federation returns a URL that encapsulates it, otherwise an error indication is
returned to the initial federation which in turn returns an error indication to the user and terminates the protocol.
4. The IMPORT request is sent by the user to the target federation. A complete URL containing the IMPORT request will typically be
created by the target federation, returned to the initial federation, and forwarded to the user as a browser redirect by the EXPORT
stage. Upon successfully validating the request, which includes an examination of the token and checking for revocation of the
identity (see dacs.acls(5)[3] for a description of how authentication/access revocation works), the target federation returns
credentials (as an HTTP cookie) that are returned to the user in the final step of the IMPORT operation - this is the end-goal of
the protocol - and the user is redirected by the target federation to an appropriate "success" URL as a convenience to the user. If
the transfer fails, no new credentials are returned and the user is redirected to an appropriate "failure" URL by the target
federation.
Implementation
The dacs_auth_transfer service implements all of the stages as separate operations of a single web service; a different implementation
might create separate services for each stage or operation, or implement a subset of the functionality (e.g., it might only support
exporting identities).
Each of the federating systems must be assigned a unique name (for DACS, through the FEDERATION_NAME directive) so that identities can
be globally unique. The federating systems need not share a common domain name suffix.
Note
In the current implementation of dacs_auth_transfer, configuration information associated with target federations is not
automatically distributed by DACS to a federation's jurisdictions. This means that only those jurisdictions that have been
specifically configured to import identities will be able to do so; a jurisdiction will not automatically understand how to
interact with a given target federation that is configured at a different jurisdiction. Each jurisdiction's administrator wanting
to provide this service must configure his site's dacs_auth_transfer service appropriately.
Details of the dacs_auth_transfer implementation and configuration requirements are now presented. A different implementation of the
protocol could look very different.
PRESENTATION
dacs_auth_transfer can emit an HTML document to prompt the user (by default, using the style sheet dacs_auth_transfer.css[4]). The
user selects an identity and target federation and submits a form. Alternatively, the information necessary to construct prompts
can be returned within an XML document that conforms to dacs_auth_transfer.dtd[5]. A site is also free to implement its own
presentation stage.
The list of known target federation names from which a user can select is obtained from mappings that have been configured at this
jurisdiction (see below).
When emitting HTML, the web page generated by dacs_auth_transfer can be customized through the auth_transfer VFS item type. The
following items are emitted if they exist:
o header: Initial HTML to emit instead of the default.
o prologue: HTML to emit immediately after the header.
o instructions: HTML to emit immediately after the prologue and before the form.
o form: Additional HTML to emit within the form. A likely use of this is to specify a hidden TRANSFER_SUCCESS_URL argument.
o epilogue: HTML to emit immediately after the form.
o trailer: Final HTML to emit instead of the default.
For example, consider the configuration directive:
VFS "[auth_transfer]dacs-fs:${Conf::DACS_HOME}/auth_transfer"
If files named header and trailer exist in the directory ${Conf::DACS_HOME}/auth_transfer, they are expected to contain the initial
and final HTML content, respectively. Note that these files consist of text and HTML markup but are not complete HTML documents.
Customization of the HTML form is possible using configuration variables:
o transfer_export_uri: the URL of the program to which the form should be submitted. By default, the URL is created from the one
used to invoke the presentation stage, which will usually be that of dacs_auth_transfer.
o transfer_submit_label: the text label to put in the form's submit button.
o transfer_submit_method: the HTTP method to use to submit the form (GET is the default).
For example, the submit button's text can be specified using the directive:
EVAL ${Conf::transfer_submit_label} = "Execute the transfer!"
EXPORT
The identity to be transferred and the name of the target federation are submitted to dacs_auth_transfer as arguments of the EXPORT
operation. The request must be accompanied by DACS credentials that match this identity and the target federation must be
recognized by the receiving jurisdiction.
For example, this URL asks the jurisdiction associated with example.com to export the identity EXAMPLE:bobo to the target
federation DSS:
https://example.com/dacs/dacs_auth_transfer?OPERATION=EXPORT
&TARGET_FEDERATION=DSS
&DACS_IDENTITY=EXAMPLE:bobo
For the request to succeed, credentials for EXAMPLE:bobo must be sent with the request, permission must be granted (by example.com)
to export the identity, example.com must be configured with an appropriate mapping, described below, such that it knows how to
submit a TOKEN request to a service associated with federation DSS, and that service must allow importation of the identity.
The mappings of federation identifiers to URLs for export purposes are provided through the AUTH_TRANSFER_EXPORT[6] directive. That
is, these mappings indicate which target federations have been configured at this jurisdiction and associate a target federation
identifier (a short, descriptive keyword) with a URL of a web service that implements the TOKEN operation for the target
federation. It is from these mappings that the list of selectable target federations is obtained.
Note
Unless jurisdictions coordinate mappings with each other, the same jurisdiction must perform both the PRESENTATION and EXPORT
operations.
For example, dacs.conf might include the directive:
AUTH_TRANSFER_EXPORT "DSS https://dacs.dss.ca/cgi-bin/dacs/dacs_auth_transfer"
This directive specifies one target federation, identified by the name DSS, and associates it with the URL of a service
implementing the TOKEN operation.
Security
The TOKEN operation must be performed over a secure communication channel, typically using SSL. URLs appearing in these
mappings should therefore specify https. The issuer of the TOKEN operation may identify itself using an SSL client certificate;
if SSL_PROG_CLIENT_CRT[7] is configured, that certificate will automatically be used.
If the issuer of the TOKEN operation possesses DACS credentials obtained offline from the target federation (e.g., using
dacscookie(1)[8]), it can specify that they be sent with the request by putting them in an object named FEDNAME.cookies
relative to the auth_transfer item type. directory ${Conf::DACS_HOME}/auth_transfer, one cookie per line. The FEDNAME filename
suffix is the federation identifier for the importing federation.
For instance, given the AUTH_TRANSFER_EXPORT directive and the VFS directive for auth_transfer above, all cookies found in a
file named /usr/local/dacs/auth_transfer/DSS.cookies would be sent with the TOKEN operation to identify the initial federation.
These cookies would have been obtained from federation DSS over a secure communication channel.
TOKEN
The syntax and semantics of a token are meaningful only to the target federation and can be changed without affecting any initial
federation. In the current implementation, the token is comprised of information such as the identity to be transferred, the
current date at the transfer federation, the client's IP address, and (optionally) the client's role string, which is encrypted
using the target federation's federation-wide key and base-64 encoded.
Note
The identity to be transferred must be a syntactically valid DACS username.
The period during which a token is valid is determined solely by the target federation. Its lifetime will ordinarily be just a few
seconds, after which it will be treated as invalid by the IMPORT stage. The AUTH_TRANSFER_TOKEN_LIFETIME_SECS[9] directive
specifies this value for dacs_auth_transfer; if not given, a compile-time default is used.
A jurisdiction within the target federation that provides identity importation must must configure at least one Transfer clause.
The transfer directives are largely analogous to the authentication and roles directives. Each Transfer element must have an id
attribute. Its value is merely a label (an alphabetic followed by zero or more alphanumerics, hyphens, and underscores) that allows
the clause to be referenced. The id attribute values must be unique (case-sensitively) within the clause's Jurisdiction section.
Security
o An access control rule must be in place to ensure that this operation can only be executed by a legitimate server belonging
to a recognized initial federation.
o The caller may not have supplied DACS credentials to identify itself and therefore the user()[10] function may not be of
use.
Transfer Clause Directives Index:
1. CREDENTIALS_LIFETIME_SECS (Optional1)
2. ERROR_URL (Optional1)
3. EXIT* (Optional1)
4. IMPORT_FROM (Required)
5. IMPORT_ROLES (Optional1)
6. IMPORT_URL (Optional1)
7. PREDICATE (Optional1)
8. REFEDERATE (Optional1)
9. ROLES* (Optional1)
10. SUCCESS_URL (Optional1)
IMPORT_FROM (Required)
This directive, which may be repeated, names an initial federation, as identified by the INITIAL_FEDERATION argument, to which
this clause applies. It must be a syntactically valid federation name. These names are case-sensitive.
REFEDERATE (Optional1)
If "yes" (case insensitive), the federation and jurisdiction of the imported identity (i.e., the DACS_IDENTITY argument) are
changed to that of the target jurisdiction. If this directive is unspecified or has another value, the original identity is
retained.
For example, if the TOKEN operation at jurisdiction ALPHA of federation FED2 is passed DACS_IDENTITY with a value of
FED1::BETA:bobo and REFEDERATE is enabled, then the imported identity will be FED2::ALPHA:bobo .
Security
This directive is useful in certain circumstances in that it can prevent a particular individual from being known by
multiple names, which may complicate access control rules. It must be used with care, however.
Say Bobo is naturally known as ALPHA:bobo within federation FED2. If she authenticates as FED1::BETA:bobo and uses
dacs_auth_transfer to obtain credentials in FED2, then by default her new credentials will be for the name FED1::BETA:bobo;
i.e., her DACS identity is retained.
Access control rules in FED2 may need to handle both names, however, which can lead to problems. Some DACS administrators
in FED2 may not even be aware of FED1, and so access to FED1::BETA:bobo may be denied while access to the same resource may
be granted to FED2::ALPHA:bobo.
If no two distinct identities in FED1 can be mapped to the same identity in FED2 (i.e., the same username component is not
associated with more than one jurisdiction that can export the identity to FED2), then the administrator at the initial
federation can advise the administrator at the target federation that the REFEDERATE directive should be enabled.
Transferred identities will then be modified to appear to have been authenticated by FED2::ALPHA. When this feature is
configured, although Bobo authenticates as FED1::BETA:bobo, her imported identity will be FED2::ALPHA:bobo.
If enabling this directive would cause two or more distinct identities to be mapped to the same DACS identity, the
directive should not be used because different individuals may be assigned the same DACS name in the target federation.
PREDICATE (Optional1)
The value of this directive is an expression. If the expression does not evaluate to True, importation will not be permitted.
CREDENTIALS_LIFETIME_SECS (Optional1)
This directive is used to override the value of the AUTH_CREDENTIALS_DEFAULT_LIFETIME_SECS[11] directive or the default.
IMPORT_ROLES (Optional1)
If "yes" (case insensitive), any roles in the existing credentials will be copied to the new credentials. The roles must be
syntactically valid at the target jurisdiction. Within the context of the clause, the variable ${Auth::IMPORTED_ROLES} is
assigned the roles string. The default is "no".
IMPORT_URL (Optional1)
This is the URL of the IMPORT stage of the protocol. By default, this is the same as that of the TOKEN stage, which is correct
for dacs_auth_transfer since it implements all stages of the protocol.
SUCCESS_URL (Optional1)
If the transfer is successful and the user has not specified another URL via the TRANSFER_SUCCESS_URL argument, the user will
be redirected to SUCCESS_URL. This directive is used by dacs_auth_transfer in the IMPORT stage.
ERROR_URL (Optional1)
If the transfer fails and the user has not specified another URL via the TRANSFER_ERROR_URL argument, the user will be
redirected to ERROR_URL. This directive is used by dacs_auth_transfer in the IMPORT stage.
ROLES* (Optional1)
The value of this directive is an expression that is evaluated at run-time. Provided an error does not occur, the resulting
string becomes the role string for the new credentials. The new role string must be syntactically valid at the target
jurisdiction. The variable ${Auth::IMPORTED_ROLES} is initialized to the role string (if any - see IMPORT_ROLES) from the
existing credentials and is assigned the value of the expression.
For example, to add fed1 to those found in the existing credentials:
IMPORT_ROLES "yes"
ROLES* '${Auth::IMPORTED_ROLES} . ",fed1"'
EXIT* (Optional1)
The value of this directive is an expression that is evaluated at run-time. Provided an error does not occur, side effects from
the evaluation may alter the final result of the clause. The variable ${Auth::IMPORTED_ROLES} is initialized to the role string
(if any - see IMPORT_ROLES) from the existing credentials and ${Auth::IMPORTED_USERNAME} is assigned the (tentative) imported
username component from the imported credentials. Either variable may be modified by the expression. The new role string must
be syntactically valid at the target jurisdiction. The new username must be syntactically valid.
This directive maps all imported usernames to guest, relative to the target jurisdiction:
EXIT* '${Auth::IMPORTED_USERNAME} = "guest"'
IMPORT
An IMPORT request is validated before being accepted, which includes examining the token and checking for revocation of the
identity. There is no guarantee that if the TOKEN operation succeeds the IMPORT operation will also.
DACS credentials imported by dacs_auth_transfer are marked as being alien and imported, the jurisdiction that executed the
importation is recorded, and the IP address associated with the user's initial credentials are associated with the new credentials;
these characteristics can be tested using the dacs.exprs(5)[10] function.
Security
An access control rule must be in place to ensure that this operation can only be executed by appropriate users. Access might
well be granted to any user but might reasonably be restricted based on IP address, etc.
To recap, assuming dacs_auth_transfer is used to transfer credentials between two DACS federations (which we will call Federation A and
Federation B) and no errors occur, the flow of control will typically be as follows:
1. The user follows a link that invokes dacs_auth_transfer at some jurisdiction within Federation A.
2. dacs_auth_transfer generates an HTML document that is displayed on the user's browser. The user selects a target federation
(Federation B) and credentials to transfer from those presented within an HTML form and submits it, invoking dacs_auth_transfer at
Federation A again, but this time to perform the EXPORT operation. The list of credentials from which the user can choose depends
on the user's current credentials in Federation A. The list of target federations depends on those known to the jurisdiction that
processes the request.
3. The dacs_auth_transfer at Federation A processes the EXPORT operation and invokes the TOKEN operation at Federation B. This action
is transparent to the user. The response from Federation B is a URL that represents a complete IMPORT operation directed at
Federation B. The EXPORT operation redirects the user's browser to that URL.
4. Upon receiving the redirect, the user's browser invokes the IMPORT operation at Federation B. Federation B returns new credentials
and redirects the user's browser to a configured or requested URL.
To interoperate with dacs_auth_transfer to import DACS credentials, a program must implement the TOKEN operation. It must also provide
functionality similar to that of the IMPORT operation. Because the TOKEN operation returns a URL encapsulating an IMPORT request to
which the client is redirected, however, the IMPORT operation can be implementation-dependent and does need to interoperate with
dacs_auth_transfer.
To interoperate with dacs_auth_transfer to export credentials to a DACS federation, a program must be capable of invoking
dacs_auth_transfer with the TOKEN operation and its arguments, and redirect the client to the URL provided by dacs_auth_transfer.
Web Service Arguments
In addition to the standard CGI arguments[12], dacs_auth_agent understands a variety of arguments that depend on the operation being
requested. The descriptions of the arguments that follow are therefore grouped by operation.
The additional arguments accepted by dacs_auth_transfer follow.
Presentation
For this stage, the value of the OPERATION argument is PRESENTATION (case insensitive).
The FORMAT argument (see dacs(1)[13]) determines the type of output, with the default being HTML.
Additional arguments:
REDIRECT_DEFAULT
If "yes" and there is exactly one set of credentials and one target federation (i.e., there is nothing for the client to select),
then automatically redirect the client to a URL representing the EXPORT stage of the protocol. Though the client will not be
required to submit a form, he will not have the opportunity to see which identity is being transferred or the name of the target
federation.
Export
For this stage, the value of the OPERATION argument is EXPORT (case insensitive).
Additional arguments:
DACS_IDENTITY
This is the identity corresponding to the credentials to be exported, expressed as a full DACS user identity (see dacs(1)[14]).
TARGET_FEDERATION
This is the jurisdiction's identifier for the federation to which the selected credentials are to be transferred. The user will
typically select this identifier from a list produced by the same jurisdiction that performs the PRESENTATION operation.
TRANSFER_SUCCESS_URL
If the transfer operation is successful, the user will be redirected to this URL.
TRANSFER_ERROR_URL
If the transfer operation fails, the user will be redirected to this URL. If unspecified, the AUTH_TRANSFER_ERROR_URL will be used
if configured, otherwise a message will be emitted.
DACS_DEBUG
If "yes", operate in a debugging mode.
Token
For this stage, the value of the OPERATION argument is TOKEN (case insensitive).
Additional arguments:
DACS_IDENTITY
The value of this argument is identical to the argument of the same name that is passed to the EXPORT stage. If the transfer
succeeds, this is the identity for which new credentials will be issued.
INITIAL_FEDERATION
This is the identifier for the federation that received the EXPORT request. The target federation must have a mapping for this
identifier.
CLIENT_ADDR
The IP address from which the EXPORT request was issued.
TRANSFER_SUCCESS_URL
If the transfer operation is successful, the user wants to be redirected to this URL. If unspecified, a default URL will be used.
TRANSFER_ERROR_URL
If the transfer operation fails, the user will be redirected to this URL. If unspecified, a default URL will be used.
DACS_DEBUG
If "yes", operate in a debugging mode.
Import
For this stage, the value of the OPERATION argument is IMPORT (case insensitive).
Additional arguments:
TOKEN
This is the value of the token returned by a previous call to the TOKEN stage of the protocol.
TRANSFER_SUCCESS_URL
If the transfer operation is successful, the user wants to be redirected to this URL. If unspecified, a default URL configured at
the target federation using the AUTH_TRANSFER_SUCCESS_URL[15] directive will be used.
TRANSFER_ERROR_URL
If the transfer operation fails, the user wants to be redirected to this URL. If unspecified, a default URL configured at the
target federation using the AUTH_TRANSFER_ERROR_URL[16] will be used.
DACS_DEBUG
If "yes", operate in a debugging mode.
EXAMPLE
The following example describes step-by-step how to configure two DACS federations, FED_EX1 (example.com) and FED_EX2 (example.net), to
enable credentials to be transferred from FED_EX1 to FED_EX2. For FED_EX1, the jurisdiction J1 (j1.example.com) will be configured to
export credentials and for FED_EX2, J2 (j2.example.net) will be configured to import credentials. The example assumes that these two
jurisdictions have already installed and configured DACS and that it is possible to authenticate (obtain credentials) somewhere within
FED_EX1.
Note
This example will not actually work without changing the domain names, URLs, and identities that it uses for demonstration purposes to
those configured for your federations and jurisdictions. Having successfully reproduced this example functionality on your systems, it
should be apparent how to extend it for additional jurisdictions and federations, and how to make credential transfer bidirectional.
1. At J1, add a jurisdiction-specific access control rule that allows dacs_auth_transfer to be used to export an identity:
<acl_rule status="enabled">
<services>
<service url_expr='"${Conf::dacs_cgi_bin_prefix}/dacs_auth_transfer"'/>
</services>
<rule order="allow,deny" pass_credentials="all">
<allow>
user("auth") and (${Args::OPERATION} eq "PRESENTATION"
or ${Args::OPERATION} eq "EXPORT")
</allow>
</rule>
</acl_rule>
At J2, add a jurisdiction-specific access control rule that allows dacs_auth_transfer to be used to import an identity:
<acl_rule status="enabled">
<services>
<service url_expr='"${Conf::dacs_cgi_bin_prefix}/dacs_auth_transfer"'/>
</services>
<rule order="allow,deny" pass_credentials="all">
<allow>
(from("j1.example.com") and ${Args::OPERATION} eq "TOKEN")
or ${Args::OPERATION} eq "IMPORT"
</allow>
</rule>
</acl_rule>
Security
In particular, the rule at the target federation must restrict access based on the identity, or possibly the IP address, associated
with the request. If the cookie-based authentication method is used, the rule would test for that specific identity.
2. At J1, configure dacs_auth_transfer to know how to invoke the TOKEN operation so that it can export credentials to FED_EX2. Add this
directive to dacs.conf:
AUTH_TRANSFER_EXPORT
"FED_EX2 https://j2.example.net/cgi-bin/dacs/dacs_auth_transfer"
Note that this is the only required additional configuration at J1.
3. At J2, configure dacs_auth_transfer so that it will import credentials from FED_EX1. Add a Transfer clause to dacs.conf:
ACCEPT_ALIEN_CREDENTIALS "yes"
<Transfer id="fed_ex1">
IMPORT_FROM "FED_EX1"
SUCCESS_URL
"https://j2.example.net/cgi-bin/dacs/dacs_current_credentials"
</Transfer>
This configuration allows credentials to be imported from federation FED_EX1. As the default, after successful importation users will
be redirected to a page that lists their identities in federation FED_EX2. In practice this might point to the site's home page, for
example. The jurisdiction must be told to recognize credentials imported from FED_EX2 using the ACCEPT_ALIEN_CREDENTIALS directive.
4. The configuration can now be tested. First, authenticate somewhere within FED_EX1 using your browser. Let's assume that you
authenticated as the identity FED_EX1::J1:bob so that this example can refer to a specific name. Invoke this URL from the browser:
https://j1.example.com/cgi-bin/dacs/dacs_auth_transfer?OPERATION=PRESENTATION
You should be presented with a web page that displays the identity FED_EX1::J1:bob (and any others that happen to be in effect) and the
target federation name FED_EX2 (and any other federations specified by a AUTH_TRANSFER_EXPORT directive). It might be instructive to
view the source for the HTML page if you are still not clear about what the PRESENTATION operation does. Click on the Transfer button
(if necessary, first selecting an identity and target federation).
One can bypass the PRESENTATION operation by directly invoking the URL:
https://j1.example.com/cgi-bin/dacs/dacs_auth_transfer?
OPERATION=EXPORT&DACS_IDENTITY=FED_EX1::J1:bob
If the transfer is successful, your browser should now possess the original credentials for the identity FED_EX1::J1:bob, valid within
FED_EX1, and credentials for the identity FED_EX1::J1:bob that are valid within FED_EX2; dacs_current_credentials, where your browser
should be redirected to in this example, should display the latter. Note that though issued by different sites, the two cookies have
the same cookie name.
The following example illustrates how an identity might be transferred from a non-DACS federation (SOME_FED) to a DACS federation (again,
FED_EX2 via its jurisdiction J2). We will assume that an appropriate access control rule has been configured at J2.
As in the previous example, at J2, configure dacs_auth_transfer so that it will import credentials from SOME_FED by adding a Transfer
clause to dacs.conf:
ACCEPT_ALIEN_CREDENTIALS "yes"
<Transfer id="some_fed">
IMPORT_FROM "SOME_FED"
REFEDERATE "YES"
IMPORT_ROLES "NO"
</Transfer>
This configuration allows credentials to be imported from federation SOME_FED.
A system administrator must write a small program, run somewhere within SOME_FED, that will invoke dacs_auth_transfer at J2 with
appropriate arguments. The program might be run automatically as part of the login procedure at SOME_FED or explicitly by providing a link
that a user can follow (e.g., labelled "Transfer Login To FED_EX2", or similar). The program simply invokes the TOKEN operation at J2 and,
if successful, redirects the user to the URL that is returned to it by dacs_auth_transfer (which represents an IMPORT operation). If the
IMPORT operation succeeds, the user will be issued an HTTP cookie bearing the DACS credentials. If desired, the URL that the user should
visit after a successful transfer can be specified through the TRANSFER_SUCCESS_URL argument.
The program might initiate the transfer by constructing and invoking a URL (via the POST method) much like this:
import_url=`http -p INITIAL_FEDERATION "SOME_FED"
-p DACS_IDENTITY "FED_EX2::J2:bobo"
-p CLIENT_ADDR 127.0.0.1
-p TRANSFER_SUCCESS_URL
"https://j2.example.net/cgi-bin/dacs/dacs_current_credentials"
-p OPERATION TOKEN
'https://j2.example.net/cgi-bin/dacs/dacs_auth_transfer'`
Here, the requested DACS identity is FED_EX2::J2:bobo. If the response looks like a URL, then the TOKEN operation succeeded; to continue
the transfer, the program must redirect the user to the URL. In this example, if credentials are returned to the user, the user will be
redirected to dacs_current_credentials by DACS (which is useful for testing but unlikely in actual use).
FILES
dacs_auth_transfer.css[4]
DIAGNOSTICS
The program exits 0 if everything was fine, 1 if an error occurred.
SEE ALSO
dacs_authenticate(8)[17], dacs_auth_agent(8)[18], dacs.conf(5)[19]
BUGS
The jurisdictional meta information should be extended to identify importing and exporting jurisdictions (e.g., as reported by
dacs_list_jurisdictions(8)[20]).
It should be possible to optionally perform comparative checks on the IP address from which the EXPORT request was issued and the IP
address from which the IMPORT request was issued. At present, if they are not identical a warning message is logged but importation is
allowed.
The current implementation is stateless on the server side. By including a nonce in the token, the possibility of replay could be further
reduced.
A mechanism for mapping imported names may be needed.
Although the credential's DACS role string is passed to the target federation, a flexible mechanism for optionally including them in the
imported credentials should be added.
The protocol should be improved with respect to peer identification for the TOKEN operation.
AUTHOR
Distributed Systems Software (www.dss.ca[21])
COPYING
Copyright2003-2012 Distributed Systems Software. See the LICENSE[22] file that accompanies the distribution for licensing information.
NOTES
1. dacsoptions
http://dacs.dss.ca/man/dacs.1.html#dacsoptions
2. ACCEPT_ALIEN_CREDENTIALS
http://dacs.dss.ca/man/dacs.conf.5.html#ACCEPT_ALIEN_CREDENTIALS
3. dacs.acls(5)
http://dacs.dss.ca/man/dacs.acls.5.html
4. dacs_auth_transfer.css
http://dacs.dss.ca/man//css/dacs_auth_transfer.css
5. dacs_auth_transfer.dtd
http://dacs.dss.ca/man/../dtd-xsd/dacs_auth_transfer.dtd
6. AUTH_TRANSFER_EXPORT
http://dacs.dss.ca/man/dacs.conf.5.html#AUTH_TRANSFER_EXPORT
7. SSL_PROG_CLIENT_CRT
http://dacs.dss.ca/man/dacs.conf.5.html#SSL_PROG_CLIENT_CRT
8. dacscookie(1)
http://dacs.dss.ca/man/dacscookie.1.html
9. AUTH_TRANSFER_TOKEN_LIFETIME_SECS
http://dacs.dss.ca/man/dacs.conf.5.html#AUTH_TRANSFER_TOKEN_LIFETIME_SECS
10. user()
http://dacs.dss.ca/man/dacs.exprs.5.html#user
11. AUTH_CREDENTIALS_DEFAULT_LIFETIME_SECS
http://dacs.dss.ca/man/dacs.conf.5.html#AUTH_CREDENTIALS_DEFAULT_LIFETIME_SECS
12. standard CGI arguments
http://dacs.dss.ca/man/dacs.services.8.html#standard_cgi_args
13. dacs(1)
http://dacs.dss.ca/man/dacs.1.html
14. dacs(1)
http://dacs.dss.ca/man/dacs.1.html#naming
15. AUTH_TRANSFER_SUCCESS_URL
http://dacs.dss.ca/man/dacs.conf.5.html#AUTH_TRANSFER_SUCCESS_URL
16. AUTH_TRANSFER_ERROR_URL
http://dacs.dss.ca/man/dacs.conf.5.html#AUTH_TRANSFER_ERROR_URL
17. dacs_authenticate(8)
http://dacs.dss.ca/man/dacs_authenticate.8.html
18. dacs_auth_agent(8)
http://dacs.dss.ca/man/dacs_auth_agent.8.html
19. dacs.conf(5)
http://dacs.dss.ca/man/dacs.conf.5.html
20. dacs_list_jurisdictions(8)
http://dacs.dss.ca/man/dacs_list_jurisdictions.8.html
21. www.dss.ca
http://www.dss.ca
22. LICENSE
http://dacs.dss.ca/man/../misc/LICENSE
DACS 1.4.27b 10/22/2012 DACS_AUTH_TRANSFER(8)