oauth_provider is ignored in pn.serve()

[marchakov-ody]

Running server using the pn.serve function with oauth_provider set:
pn.serve(app, oauth_provider='custom', cookie_secret='...')
does not provide oauth_provider value to opts, so the server runs as if it has no oauth_provider configured (regardless of the oauth_provider value - it can be custom or any of the default providers).
If show=True argument for pn.serve() is provided, the server attempts to open /login page, but returns the 404: Not Found page and the following message in the console:
WARNING:tornado.access:404 GET /login (::1) 0.00ms

The problem seems to be caused by panel/io/server.py code, as was mentioned in this comment. As suggested in the same comment, replacing

 if config.oauth_provider:
     from ..auth import OAuthProvider
     opts['auth_provider'] = OAuthProvider()
 if oauth_provider:
     config.oauth_provider = oauth_provider

with

 if oauth_provider:
        from ..auth import OAuthProvider
        config.oauth_provider = oauth_provider
        opts["auth_provider"] = OAuthProvider()

seems to fix the issue.

[BiswajitTri]

if you are using pn.serve() then oauth attributes can be set with pn.config