By default Weblogic DefaultAuthenticator’s JAAS Control flag has been set as REQUIRED.
what that means is, if you have any other authenticators configured then, the userId must pass through the DefaultAuthenticator else it will fail and this will not be evident in the default logs available so please set it to OPTIONAL.
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More on JAAS control flag,
Returns how the login sequence uses the Authentication provider.
A REQUIRED value specifies this LoginModule must succeed. Even if it fails, authentication proceeds down the list of LoginModules for the configured Authentication providers. This setting is the default.
A REQUISITE value specifies this LoginModule must succeed. If other Authentication providers are configured and this LoginModule succeeds, authentication proceeds down the list of LoginModules. Otherwise, control is return to the application.
A SUFFICIENT value specifies this LoginModule need not succeed. If it does succeed, return control to the application. If it fails and other Authentication providers are configured, authentication proceeds down the LoginModule list.
An OPTIONAL value specifies this LoginModule need not succeed. Whether it succeeds or fails, authentication proceeds down the LoginModule list.