GUACAMOLE-839: Ensure all SSO and related mechanisms set Credentials username.

This is necessary to ensure the ${GUAC_USERNAME} token is properly
substituted in cases where SSO and SSO-like auth methods are used.

extensions/guacamole-auth-sso/modules/guacamole-auth-sso-saml/src/main/java/org/apache/guacamole/auth/saml/AuthenticationProviderService.java

@@ -96,15 +96,9 @@ public class AuthenticationProviderService implements SSOAuthenticationProviderS
                 getSessionIdentifier(credentials));
 
         if (identity != null) {
-
-            // Back-port the username to the credentials
-            credentials.setUsername(identity.getUsername());
-
-            // Configure the AuthenticatedUser and return it
             SAMLAuthenticatedUser authenticatedUser = authenticatedUserProvider.get();
             authenticatedUser.init(identity, credentials);
             return authenticatedUser;
-
         }
 
         // Redirect to SAML IdP if no SAML identity is associated with the