This problem occures/happends, because of the way how the session authentication method (SAML AuthnRequest) is configured on the other SSO app. WritebackExtreme by defaults use “Password, ProtectedTransport” as request authentication method.
Solution
Since WritebackExtreme 1.7.3 we have added an environment variable to allow all options, but allow any cross request authentication method.
Within the `.env` file set `PORTAL_SAML_REQUESTED_AUTH=false` to not strictly check on the cross request authentication method.
Note: In future versions this could be made configurable.