Add new provider - SAML via Azure AD

[greenpau]

Currently, the is no SAML backend. I want to open this issue to work on it to support Azure AD workflow.

In Azure, there is an ability to create an application registration. When Azure users click on the icon associated with the application, they get redirected to a configurable URL, e.g. caddy proxy.

The redirected response could be a POST containing SAML payload.

Here, in case of AWS, it looks like this.

Once the caddy plugin gets the request, it validates the SAML payload and logs the user in.