Authorization endpoint MUST allow to use `GET` according to RFC

[nshkg]

The https://tools.ietf.org/html/rfc6749#section-3.1 talks:

The authorization server MUST support the use of the HTTP "GET method [RFC2616] for the authorization endpoint and MAY support the use of the "POST" method as well.

However if i will try to use GETserver respond with 401 - You must pass resource owner credential via POST