def METHOD_NAME(request):
    # Update authorization flow from previously stored state in AuthFlowUuid instance in mymedicare_login().
    request_state = request.GET.get('relay')
    clear_session_auth_flow_trace(request)
    update_session_auth_flow_trace_from_state(request, request_state)
    # SLSx client instance
    slsx_client = OAuth2ConfigSLSx()
    request_token = request.GET.get('req_token', None)
    slsx_client.validate_asserts(request, [
        (request_token is None, "SLSx request_token is missing in callback error.")
    ], MedicareCallbackExceptionType.VALIDATION_ERROR)
    # Exchange req_token for access token
    slsx_client.exchange_for_access_token(request_token, request)
    # Get user_info. TODO: Move userinfo type validations in to this method.
    # get_user_info() will do validation, and then populate values from user info
    # e.g. first last name, email, sub (user_id), hicn, mbi, and their hashes etc.
    slsx_client.get_user_info(request)
    # Signout bene to prevent SSO issues per BB2-544
    slsx_client.user_signout(request)
    # Validate bene is signed out per BB2-544
    slsx_client.validate_user_signout(request)
    # Log successful identity information gathered.
    slsx_client.log_event(request, {})
    # Find or create the user associated with the identity information from SLS.
    user, crosswalk_action = get_and_update_user(slsx_client, request=request)
    # Set crosswalk_action and get auth flow session values.
    set_session_auth_flow_trace_value(request, 'auth_crosswalk_action', crosswalk_action)
    # Log successful authentication with beneficiary when we return back here.
    slsx_client.log_authn_success(request, {
        "user": {
            "id": user.id,
            "username": user.username,
            "crosswalk": {
                "id": user.crosswalk.id,
                "user_hicn_hash": user.crosswalk.user_hicn_hash,
                "user_mbi_hash": user.crosswalk.user_mbi_hash,
                "fhir_id": user.crosswalk.fhir_id,
                "user_id_type": user.crosswalk.user_id_type,
            },
        },
    })
    # Update request user.
    request.user = user