External authentication

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

@@ -2,6 +2,7 @@ package emu.grasscutter.auth;
 
 import emu.grasscutter.server.http.objects.*;
 import express.http.Request;
+import express.http.Response;
 import lombok.AllArgsConstructor;
 import lombok.Builder;
 import lombok.Getter;
@@ -52,12 +53,20 @@ public interface AuthenticationSystem {
      */
     Authenticator<ComboTokenResJson> getSessionKeyAuthenticator();
 
+    /**
+     * This is the authenticator used for handling external authentication requests.
+     * @return An authenticator.
+     */
+    ExternalAuthenticator getExternalAuthenticator();
+
     /**
      * A data container that holds relevant data for authenticating a client.
      */
     @Builder @AllArgsConstructor @Getter
     class AuthenticationRequest {
         private final Request request;
+        @Nullable private final Response response;
+        
         @Nullable private final LoginAccountRequestJson passwordRequest;
         @Nullable private final LoginTokenRequestJson tokenRequest;
         @Nullable private final ComboTokenReqJson sessionKeyRequest;
@@ -104,4 +113,15 @@ public interface AuthenticationSystem {
                 .sessionKeyData(tokenData)
                 .build();
     }
+
+    /**
+     * Generates an authentication request from a {@link Response} object.
+     * @param request The Express request.
+     * @param response the Express response.
+     * @return An authentication request.
+     */
+    static AuthenticationRequest fromExternalRequest(Request request, Response response) {
+        return AuthenticationRequest.builder().request(request)
+                .response(response).build();
+    }
 }

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

@@ -15,6 +15,7 @@ public final class DefaultAuthentication implements AuthenticationSystem {
     private final Authenticator<LoginResultJson> passwordAuthenticator = new PasswordAuthenticator();
     private final Authenticator<LoginResultJson> tokenAuthenticator = new TokenAuthenticator();
     private final Authenticator<ComboTokenResJson> sessionKeyAuthenticator = new SessionKeyAuthenticator();
+    private final ExternalAuthenticator externalAuthenticator = new ExternalAuthentication();
     
     @Override
     public void createAccount(String username, String password) {
@@ -46,4 +47,9 @@ public final class DefaultAuthentication implements AuthenticationSystem {
     public Authenticator<ComboTokenResJson> getSessionKeyAuthenticator() {
         return this.sessionKeyAuthenticator;
     }
+
+    @Override
+    public ExternalAuthenticator getExternalAuthenticator() {
+        return this.externalAuthenticator;
+    }
 }

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

@@ -158,4 +158,24 @@ public final class DefaultAuthenticators {
             return response;
         }
     }
+
+    /**
+     * Handles authentication requests from external sources.
+     */
+    public static class ExternalAuthentication implements ExternalAuthenticator {
+        @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 handleAccountCreation(AuthenticationRequest request) {
+            assert request.getResponse() != null;
+            request.getResponse().send("Authentication is not available with the default authentication method.");
+        }
+
+        @Override public void handlePasswordReset(AuthenticationRequest request) {
+            assert request.getResponse() != null;
+            request.getResponse().send("Authentication is not available with the default authentication method.");
+        }
+    }
 }

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

@@ -0,0 +1,33 @@
+package emu.grasscutter.auth;
+
+import emu.grasscutter.auth.AuthenticationSystem.AuthenticationRequest;
+
+/**
+ * Handles authentication via external routes.
+ */
+public interface ExternalAuthenticator {
+
+    /**
+     * Called when an external login request is made.
+     * @param request The authentication request.
+     */
+    void handleLogin(AuthenticationRequest request);
+
+    /**
+     * Called when an external account creation request is made.
+     * @param request The authentication request.
+     *                
+     * For developers: Use {@link AuthenticationRequest#getRequest()} to get the request body.
+     *                 Use {@link AuthenticationRequest#getResponse()} to get the response body.
+     */
+    void handleAccountCreation(AuthenticationRequest request);
+
+    /**
+     * Called when an external password reset request is made.
+     * @param request The authentication request.
+     *                
+     * For developers: Use {@link AuthenticationRequest#getRequest()} to get the request body.
+     *                 Use {@link AuthenticationRequest#getResponse()} to get the response body.
+     */
+    void handlePasswordReset(AuthenticationRequest request);
+}