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OpenAM centralizes authentication by using a variety of authentication modules. authentication modules connect to identity repositories that store identities and provide authentication services. The identity repositories can be implemented as LDAP directories, relational databases, RADIUS, Windows authentication, one-time password services, other standards-based access management systems and much more.

OpenAM centralizes authorization by letting you use OpenAM to manage access policies separate from applications and resources. Instead of building access policy into a web application, you install a policy agent with the web application to request policy decisions from OpenAM. This way you can avoid issues that could arise when developers must embed policy decisions into their applications. With OpenAM, if policy changes or an issue is found after the application is deployed, you have only to change the policy definition in OpenAM, not deploy a new version of the application. OpenAM makes the authorization decisions, and policy agents enforce the decisions on OpenAM's behalf.

Bridging the SAML and OAuth 2.0 frameworks is a well understood problem. The following stack of IETF specs provides a standard solution: If you look at the core OAuth 2.0 spec (RFC 6749) and its token endpoint definition - this is basically an OAuth server endpoint which returns an access token in exchange for a "grant" -- an open-ended concept of something deemed appropriate to grant the client app the issue of an access token. In the typical OAuth scenario this is an authorisation code signifying that the user has been previously authenticated and given their consent. But the grant could also be something else. There is a further IETF spec called draft-ietf-oauth-assertions-16 that builds on the core RFC 6749 standard which says that the grant can also be an assertion (a signed proof of something) and defines the necessary token request parameters for that. Finally, there is draft-ietf-oauth-saml2-bearer-20, which specifies how this assertion can be a SAML 2.0 Bearer Assertion. This standard mechanism for converting a SAML assertion into an OAuth 2.0 access token is essentially all that is needed to bridge the two frameworks. To ensure removal of users is properly reflected by the authorisation systems there are two approaches, which can be combined: Make the OAuth 2.0 access tokens short lived. This will force the client to repeat the authorisation process when the token expires, and if the user no longer exists authentication will fail and no grant (SAML assertion) will be issued. Provide an API for revoking issued OAuth 2.0 access tokens, see RFC 7009 for details.

An authentication service confirms the identity of a user or a client application.

OpenAM is most frequently used to protect web-accessible resources. Users browse to a protected web application page. An agent installed on the server with the web application redirects the user to OpenAM for access management. OpenAM determines who the user is, and whether the user has the right to access the protected page. OpenAM then redirects the user back to the protected page, with authorization credentials that can be verified by the agent. The agent allows OpenAM authorized users access the page.

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