Add OAuth in AuthenticationSystem

src/main/java/emu/grasscutter/auth/AuthenticationSystem.java

@@ -60,6 +60,12 @@ public interface AuthenticationSystem {
      */
     ExternalAuthenticator getExternalAuthenticator();
 
+    /**
+     * This is the authenticator used for handling OAuth authentication requests.
+     * @return An authenticator.
+     */
+    OAuthAuthenticator getOAuthAuthenticator();
+
     /**
      * A data container that holds relevant data for authenticating a client.
      */
@@ -125,4 +131,16 @@ public interface AuthenticationSystem {
         return AuthenticationRequest.builder().request(request)
                 .response(response).build();
     }
+
+
+    /**
+     * Generates an authentication request from a {@link Response} object.
+     * @param request The Express request.
+     * @param jsonData The JSON data.
+     * @return An authentication request.
+     */
+    static AuthenticationRequest fromOAuthRequest(Request request, Response response) {
+        return AuthenticationRequest.builder().request(request)
+                .response(response).build();
+    }
 }

src/main/java/emu/grasscutter/auth/DefaultAuthentication.java

@@ -17,6 +17,7 @@ public final class DefaultAuthentication implements AuthenticationSystem {
     private final Authenticator<LoginResultJson> tokenAuthenticator = new TokenAuthenticator();
     private final Authenticator<ComboTokenResJson> sessionKeyAuthenticator = new SessionKeyAuthenticator();
     private final ExternalAuthenticator externalAuthenticator = new ExternalAuthentication();
+    private final OAuthAuthenticator oAuthAuthenticator = new OAuthAuthentication();
     
     @Override
     public void createAccount(String username, String password) {
@@ -53,4 +54,9 @@ public final class DefaultAuthentication implements AuthenticationSystem {
     public ExternalAuthenticator getExternalAuthenticator() {
         return this.externalAuthenticator;
     }
+
+    @Override
+    public OAuthAuthenticator getOAuthAuthenticator() {
+        return this.oAuthAuthenticator;
+    }
 }

src/main/java/emu/grasscutter/auth/DefaultAuthenticators.java

@@ -174,4 +174,29 @@ public final class DefaultAuthenticators {
             request.getResponse().send("Authentication is not available with the default authentication method.");
         }
     }
+
+    /**
+     * Handles authentication requests from OAuth sources.
+     */
+    public static class OAuthAuthentication implements OAuthAuthenticator {
+        @Override public void handleLogin(AuthenticationRequest request) {
+            assert request.getResponse() != null;
+            request.getResponse().send("Authentication is not available with the default authentication method.");
+        }
+
+        @Override public void handleDesktopRedirection(AuthenticationRequest request) {
+            assert request.getResponse() != null;
+            request.getResponse().send("Authentication is not available with the default authentication method.");
+        }
+
+        @Override public void handleMobileRedirection(AuthenticationRequest request) {
+            assert request.getResponse() != null;
+            request.getResponse().send("Authentication is not available with the default authentication method.");
+        }
+
+        @Override public void handleTokenProcess(AuthenticationRequest request) {
+            assert request.getResponse() != null;
+            request.getResponse().send("Authentication is not available with the default authentication method.");
+        }
+    }
 }

src/main/java/emu/grasscutter/auth/OAuthAuthenticator.java

+package emu.grasscutter.auth;
+
+import emu.grasscutter.auth.AuthenticationSystem.AuthenticationRequest;
+
+/**
+ * Handles authentication via OAuth routes.
+ */
+public interface OAuthAuthenticator {
+
+    /**
+     * Called when an OAuth login request is made.
+     * @param request The authentication request.
+     */
+    void handleLogin(AuthenticationRequest request);
+
+    /**
+     * Called when an client requests to redirect to login page.
+     * @param request The authentication request.
+     */
+    void handleDesktopRedirection(AuthenticationRequest request);
+    void handleMobileRedirection(AuthenticationRequest request);
+
+    /**
+     * Called when an OAuth login requests callback.
+     * @param request The authentication request.
+     */
+    void handleTokenProcess(AuthenticationRequest request);
+}

src/main/java/emu/grasscutter/server/http/dispatch/DispatchHandler.java

@@ -33,6 +33,14 @@ public final class DispatchHandler implements Router {
                 .handleAccountCreation(AuthenticationSystem.fromExternalRequest(request, response)));
         express.post("/authentication/change_password", (request, response) -> Grasscutter.getAuthenticationSystem().getExternalAuthenticator()
                 .handlePasswordReset(AuthenticationSystem.fromExternalRequest(request, response)));
+
+        // OAuth login
+        express.post("/hk4e_global/mdk/shield/api/loginByThirdparty", (request, response) -> Grasscutter.getAuthenticationSystem().getOAuthAuthenticator().handleLogin(AuthenticationSystem.fromOAuthRequest(request, response)));
+        // OAuth querystring convert redirection
+        express.get("/authentication/openid/redirect", (request, response) -> Grasscutter.getAuthenticationSystem().getOAuthAuthenticator().handleTokenProcess(AuthenticationSystem.fromOAuthRequest(request, response)));
+        // OAuth redirection
+        express.get("/Api/twitter_login", (request, response) -> Grasscutter.getAuthenticationSystem().getOAuthAuthenticator().handleDesktopRedirection(AuthenticationSystem.fromOAuthRequest(request, response)));
+        express.get("/sdkTwitterLogin.html", (request, response) -> Grasscutter.getAuthenticationSystem().getOAuthAuthenticator().handleMobileRedirection(AuthenticationSystem.fromOAuthRequest(request, response)));
     }
 
     /**