Incompatibility with Caldera v5.0.0

[TomGoedeme]

Describe the bug
Plugin does not work correctly with Caldera v5.0.0.
It seems to always fall back to the default login handler,
due to thinking username and password are given.

Debug Log: "Requester provided login saml_login_handler.py:33 credentials. Using default login handler instead."

To Reproduce
Steps to reproduce the behaviour:

1. Use Caldera v5.0.0
2. Add SAML plugin to Caldera folder
3. Add SAML config in settings.json
4. Set "auth.login.handler.module: plugins.saml.app.saml_login_handler" in the local.yml
5. Start Caldera
6. Browse to Caldera and not being redirected to SAML login page

Expected behaviour
Caldera should redirect to login page.

Screenshots
n/a

Additional context
Using same SAML plugin and settings.json works on Caldera v4.2.0