If the received token is successfully validated, and if the client supplies a TokenType in the request that does not correspond to the WS-Trust "status" namespace, then the TokenValidateOperation attempts to transform the validated token into a token of the requested type. Token transformation works in a similar way to token issuing, as detailed previously. A TokenProviderParameters object is constructed and the same processing steps (Realm parsing, AppliesTo parsing) are followed as for token issuing.
One additional processing step occurs before the token is transformed. If the TokenValidatorResponse object has a principal that was set by the TokenValidator implementation, then it is set as the principal of the TokenProviderParameters object. However, it is possible that the token is being issued in a different realm to that of the validated token, and the principal might also need to be transformed. Recall that the STSPropertiesMBean configuration object defined on AbstractOperation has an IdentityMapper property. This interface is used to map identities across realms. It has a single method:
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Principal mapPrincipal(String sourceRealm, Principal sourcePrincipal, String targetRealm)- Map a principal from a source realm to a target realm
If the source realm is not null (the realm of the validated token as returned in TokenValidatorResponse), and if it does not equal the target realm (as set by the RealmParser), then the identity mapper is used to map the principal to the target realm and this is stored in TokenProviderParameters for use in token generation. After the (optional) identity mapping step, TokenValidateOperation iterates through the TokenProvider list to find an implementation that can "handle" the desired token type in the given (target) realm (if applicable). If no TokenProvider is defined, or if no TokenProvider can handle the desired token type, then an exception is thrown.