Add swagger UI oauth2 redirect page

[steinitzu]

I added the oauth2 redirect page from swagger-ui (html/js copied from https://github.com/swagger-api/swagger-ui/blob/master/dist/oauth2-redirect.html )
It's mounted to the app under /{docs_url}/oauth2-redirect

This is needed for implicit grant Oauth2 flow in swagger ui, so it can grab the token on redirect, e.g. this kind of security scheme:

from fastapi.security import OAuth2
from fastapi.openapi.models import OAuthFlows, OAuthFlowImplicit

oauth2_scheme = OAuth2(
    flows=OAuthFlows(
        implicit=OAuthFlowImplicit(
            authorizationUrl="https://some/oauth2/provider/login/url"
        )
    )
)

[codecov]

Codecov Report

Merging #198 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #198   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files         175    177    +2     
  Lines        4268   4327   +59     
=====================================
+ Hits         4268   4327   +59

Impacted Files	Coverage Δ
tests/test_custom_swagger_ui_redirect.py	100% <100%> (ø)
tests/test_no_swagger_ui_redirect.py	100% <100%> (ø)
fastapi/applications.py	100% <100%> (ø)	⬆️
fastapi/openapi/docs.py	100% <100%> (ø)	⬆️
tests/test_application.py	100% <100%> (ø)	⬆️

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[tiangolo]

Thanks! Interesting. I'll check it soon.

[tiangolo]

Thank you @steinitzu !

I just updated/refactored it a bit, to make it optional and to make the URL path for the redirection parameterizable.

It is now merged! 🎉 🚀