Add support for Authorization POST request

[AnuradhaSK]

Describe the issue:
Currently, SDK supports only sending HTTP GET request to Authorization Endpoint. POST requests also need to be supported as per the specification . https://openid.net/specs/openid-connect-core-1_0.html#AuthRequest

 POST /authorize HTTP/1.1
  Host: server.example.com
  Content-Type: application/x-www-form-urlencoded

  response_type=code
    &scope=openid
    &client_id=s6BhdRkqt3
    &redirect_uri=https%3A%2F%2Fclient.example.org%2Fcb