Identity assertion to the downstream server

When a client authenticates to a server, the received credential is set. When the authorization engine checks the credential to determine whether access is permitted, it also sets the invocation credential. Identity assertion is the invocation credential asserted to the downstream server. Depending on the RunAs mode for the enterprise beans, the invocation credential is set as the originating client identity, the server identity, or a specified different identity. Regardless of the identity that is set, when identity assertion is enabled, it is the invocation credential that is asserted to the downstream server.

The invocation credential identity is sent to the downstream server in an identity token. In addition, the sending server identity, including the password or token, is sent in the client authentication token when basic authentication is enabled. The sending server identity is sent through an SSL client certification authentication when client certificate authentication is enabled. Basic authentication takes precedence over client certificate authentication.

Both identity tokens are needed by the receiving server to accept the asserted identity. The receiving server completes the following actions to accept the asserted identity:

• The identity of the sending server sent to the receiving server is either a GSSUP token (user ID and password) or an SSL client certificate.

• Trust is established between the sending and receiving server depending on what identity is being sent.

  1. When a GGSUP token is sent, the trust is established by verifying that the sending server identity is on the trusted principal list of the receiving server.

  2. When an SSL client certificate is sent

     The trust is established by verifying that this user ID has the UPDATE authority to the CB.BIND.<servername> profile.

• After it is determined that the sending server is on the trusted list, the server authenticates the sending server to verify its identity.

• The server is authenticated by comparing the user ID and password from the sending server to the receiving server. If the credentials of the sending server are authenticated and trusted, then the server proceeds to evaluate the identity token.

• The receiving server checks its defined user registry for the presence of the asserted user ID to gather more credential information for authorization purposes (for example, group memberships). Thus, the receiving server's user registry must contain all of the asserted user IDs. Otherwise, identity assertion is not possible. In a stateful server, this action occurs once for the sending server and the receiving server pair where the identity tokens are the same. Subsequent requests are made through a session ID.

  When the downstream server does not have a user registry with access to the asserted user IDs in its repository, do not use identity assertion because authorization checks will fail. By disabling identity assertion, the authorization checks on the receiving server are not needed.

Evaluation of the identity token consists of the following four identity formats that exist in an identity token

• Principal name
• Distinguished name
• Certificate chain
• Anonymous identity

The product servers that receive authentication information typically support all four identity types. The sending server decides which one is chosen, based on how the original client authenticated. The existing type depends on how the client originally authenticates to the sending server. For example, if the client uses SSL client authentication to authenticate to the sending server, then the identity token sent to the downstream server contains the certificate chain. With this information, the receiving server can perform its own certificate chain mapping and interoperability is increased with other vendors and platforms.

After the identity format is understood and parsed, the identity maps to a credential. For an ITTPrincipal identity token, this identity maps one-to-one with the user ID fields.

For an ITTDistinguishedName identity token, the mapping depends on the user registry. For LDAP, the configured search filter determines how the mapping occurs. For LocalOS, the first attribute of the distinguished name (DN), which is typically the same as the common name, maps to the user ID of the registry.

Identity assertion is only available using the Common Secure Interoperability v2 (CSIv2) protocol.

There is a restriction for using identity assertion with KRB token to downstream. If we use identity assertion with Kerberos enabled, the identity assertion does not have the Kerberos authentication token (KRBAuthnToken) when going to downstream servers. It uses LTPA for authentication instead.

Authenticating users

(ZOS) Distributed identity filters configuration in z/OS security