get_oidp_metadata assumes that the issuer URL has no path

[Clemens-Toegel]

When having an OpenID Connect issuer with a path (e.g.: https://your.authentik.example.org/application/o/your-app-slug/), the synapse token authenticator can not find the OpenIDProviderMetadata as urljoin strips away the path.

Expected Behavior

get_oidp_metadata respects the given path from the issuer URL

Current Behavior

get_oidp_metadata strips away the path from the URL

Possible Solution

Current implementation:

synapse-token-authenticator/synapse_token_authenticator/utils.py

Line 21 in f4d339f

urljoin(issuer, "/.well-known/openid-configuration"),

Solution:
The urljoin should add the well known part without a trailing slash to avoid stripping the issuer URL:
urljoin(issuer, ".well-known/openid-configuration")