Conversion to a dict loses repeated keys in query string

https://github.com/apache/infrastructure-oauth/blob/21d687c822ca84bc6aa8872c09aa99d5c9da2bde/app/endpoints/oauth.py#L71

If a query string contains repeated parameter keys, only one will be kept because of the conversion to a dict.

Whilst having repeated keys is unusual, it is allowed by the syntax.
Note that `parse_qsl` returns a list (rather than a dict) in order to allow for this.

Start at app/endpoints/oauth.py around line 71 and inspect how parse_qsl output is converted before the OAuth request is handled. Verify the behavior with a query string containing repeated parameter keys; done means all occurrences are preserved rather than one being discarded.

Written by the indexing model from the issue text.