Add support for Authorization POST request

**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
```

Start by locating the SDK's existing Authorization Endpoint GET request handling and compare it with the OpenID Connect Core 1.0 AuthRequest specification linked in the issue. Trace how request parameters are assembled and verify that the completed work supports the form-encoded POST example while preserving the existing GET behavior.

Written by the indexing model from the issue text.