Refactor OAuth2 Provider Authorization Flow

This PR refactors the OAuth2 provider authorization flow by:

1. Removing theauthorizeMW middleware and directly implementing its functionality in theShowAuthorizePage handler
2. Simplifying function signatures by removing unnecessary parameters:
   • Removeddb parameter fromShowAuthorizePage
   • RemovedaccessURL parameter fromProcessAuthorize
3. Changing the redirect status code inProcessAuthorize from 307 (Temporary Redirect) to 302 (Found) to improve compatibility with external OAuth2 apps and browsers. (Technical explanation: we replied with a 307 to a POST request, thus the browser performs a redirect to that URL as a POST request, but we need it to be a GET request to be compatible. Thus, we use the 302 redirect so that browsers turn it into a GET request when redirecting back to the redirect_uri.)

The changes maintain the same functionality while simplifying the code and improving compatibility with external systems.