Move AS registration handling to dedicated function and split the switch/case to avoid unnecessary condition

src/github.com/matrix-org/dendrite/clientapi/routing/register.go

@@ -535,7 +535,7 @@ func handleRegistrationFlow(
 		// Add SharedSecret to the list of completed registration stages
 		sessions.AddCompletedStage(sessionID, authtypes.LoginTypeSharedSecret)
 
-	case "", authtypes.LoginTypeApplicationService:
+	case "":
 		// Extract the access token from the request, if there's one to extract
 		// (which we can know by checking whether the error is nil or not).
 		accessToken, err := auth.ExtractAccessToken(req)
@@ -544,13 +544,52 @@ func handleRegistrationFlow(
 		// an AS or the request is made as the first step of a registration
 		// using the User-Interactive Authentication API. This can be determined
 		// by whether the request contains an access token.
-		if err == nil || r.Auth.Type != "" {
+		if err == nil {
-			// If the auth type explicitely relates to Application Services but
+			return handleApplicationServiceRegistration(
+				accessToken, err, req, r, cfg, accountDB, deviceDB,
+			)
+		}
+
+	case authtypes.LoginTypeApplicationService:
+		accessToken, err := auth.ExtractAccessToken(req)
+		return handleApplicationServiceRegistration(
+			accessToken, err, req, r, cfg, accountDB, deviceDB,
+		)
+
+	case authtypes.LoginTypeDummy:
+		// there is nothing to do
+		// Add Dummy to the list of completed registration stages
+		sessions.AddCompletedStage(sessionID, authtypes.LoginTypeDummy)
+
+	default:
+		return util.JSONResponse{
+			Code: http.StatusNotImplemented,
+			JSON: jsonerror.Unknown("unknown/unimplemented auth type"),
+		}
+	}
+
+	// Check if the user's registration flow has been completed successfully
+	// A response with current registration flow and remaining available methods
+	// will be returned if a flow has not been successfully completed yet
+	return checkAndCompleteFlow(sessions.GetCompletedStages(sessionID),
+		req, r, sessionID, cfg, accountDB, deviceDB)
+}
+
+func handleApplicationServiceRegistration(
+	accessToken string,
+	tokenErr error,
+	req *http.Request,
+	r registerRequest,
+	cfg *config.Dendrite,
+	accountDB *accounts.Database,
+	deviceDB *devices.Database,
+) util.JSONResponse {
+	// If the auth type explicitly relates to Application Services but
 	// there's no access token provided, return an error.
-			if err != nil {
+	if tokenErr != nil {
 		return util.JSONResponse{
 			Code: http.StatusUnauthorized,
-					JSON: jsonerror.MissingToken(err.Error()),
+			JSON: jsonerror.MissingToken(tokenErr.Error()),
 		}
 	}
 
@@ -572,25 +611,6 @@ func handleRegistrationFlow(
 	)
 }
 
-	case authtypes.LoginTypeDummy:
-		// there is nothing to do
-		// Add Dummy to the list of completed registration stages
-		sessions.AddCompletedStage(sessionID, authtypes.LoginTypeDummy)
-
-	default:
-		return util.JSONResponse{
-			Code: http.StatusNotImplemented,
-			JSON: jsonerror.Unknown("unknown/unimplemented auth type"),
-		}
-	}
-
-	// Check if the user's registration flow has been completed successfully
-	// A response with current registration flow and remaining available methods
-	// will be returned if a flow has not been successfully completed yet
-	return checkAndCompleteFlow(sessions.GetCompletedStages(sessionID),
-		req, r, sessionID, cfg, accountDB, deviceDB)
-}
-
 // checkAndCompleteFlow checks if a given registration flow is completed given
 // a set of allowed flows. If so, registration is completed, otherwise a
 // response with