code: @Nullable
    public static IAuthSubject getSubjectFromCredentials (@Nonnull final IAuthCredentials aCredentials)
    {
      for (final IAuthCredentialToSubjectResolverSPI aHdl : s_aHdlList)
        if (aHdl.supportsCredentials (aCredentials))
        {
          final IAuthSubject aSubject = aHdl.getSubjectFromCredentials (aCredentials);
          if (aSubject != null)
            return aSubject;
        }
      return null;
    }
docs: Resolve the {@link IAuthSubject} from the specified credentials.
  
  @param aCredentials
  The credentials to be transformed.
  @return <code>null</code> if no subject matches the specified credentials.