add an option in oauth2-redirect.html to use the HTTP Basic authentication scheme for the client secret

As recommended in RFC, client secret should be transmitted using Basic authentication. Using swagger-ui with an oauth2 server that only supports this security scheme for client authentication returns an error.

Using OAuth2 with the authorization code grant type, the request sent by swagger ui using oauth2-redirect.html is as follow:

POST /token HTTP/1.1
Host: localhost:8090
Content-Type: application/x-www-form-urlencoded

grant_type=authorization_code&code=XXXXXX&client_id=YYYYYY&client_secret=ZZZZZZ&redirect_uri=http%3A%2F%2Flocalhost%3A8091%2Foauth2-redirect.html

I would like to have the possibility to force the Basic auth in the oauth2-redirect.html:

POST /token HTTP/1.1
Host: localhost:8090
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded

grant_type=authorization_code&code=XXXXXX&redirect_uri=http%3A%2F%2Flocalhost%3A8091%2Foauth2-redirect.html

Start by reading oauth2-redirect.html and trace how the authorization-code token request is assembled. Add an option that sends the client credentials with HTTP Basic authentication instead of including them in the form body, then verify that the generated request matches the requested Authorization header and omits the client secret form field.