Fix returned error in authentication code flow

[garciasolero]

What type of PR is this?

• correction

What this PR does / why we need it:

According to OAuth 2.0 (RFC 6749), if the resource owner denies the request, the response should redirect the user-agent to the client redirection URI by adding the error parameter with access_denied value.

If the resource owner denies the access request or if the request fails for reasons other than a missing or invalid redirection URI, the authorization server informs the client by adding the following parameters to the query component of the redirection URI using the"application/x-www-form-urlencoded" format [...]

Which issue(s) this PR fixes:

Special notes for reviewers:

Changelog input

Additional documentation

[jpengar]

LGTM. Good catch! That was a doc typo.

[sebdewet]

LGTM !