feat: add GitHub OAuth2 authentication support

frontend/src/app/feature/auth/login/login.component.html

@@ -82,8 +82,26 @@
         </button>
       </div>
     </form>
+    
+    <div class="my-4 flex items-center">
+      <div class="flex-grow h-px bg-deep-blue-light/30"></div>
+      <span class="px-3 text-xs text-text-secondary">ODER</span>
+      <div class="flex-grow h-px bg-deep-blue-light/30"></div>
+    </div>
+    
+    <div class="mb-4">
+      <button 
+        (click)="loginWithGithub()" 
+        class="w-full py-2.5 px-4 rounded flex items-center justify-center bg-gray-800 hover:bg-gray-700 text-white transition-colors"
+      >
+        <svg class="h-5 w-5 mr-2" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="currentColor">
+          <path d="M12 0C5.37 0 0 5.37 0 12c0 5.31 3.435 9.795 8.205 11.385.6.105.825-.255.825-.57 0-.285-.015-1.23-.015-2.235-3.015.555-3.795-.735-4.035-1.41-.135-.345-.72-1.41-1.23-1.695-.42-.225-1.02-.78-.015-.795.945-.015 1.62.87 1.845 1.23 1.08 1.815 2.805 1.305 3.495.99.105-.78.42-1.305.765-1.605-2.67-.3-5.46-1.335-5.46-5.925 0-1.305.465-2.385 1.23-3.225-.12-.3-.54-1.53.12-3.18 0 0 1.005-.315 3.3 1.23.96-.27 1.98-.405 3-.405s2.04.135 3 .405c2.295-1.56 3.3-1.23 3.3-1.23.66 1.65.24 2.88.12 3.18.765.84 1.23 1.905 1.23 3.225 0 4.605-2.805 5.625-5.475 5.925.435.375.81 1.095.81 2.22 0 1.605-.015 2.895-.015 3.3 0 .315.225.69.825.57A12.02 12.02 0 0 0 24 12c0-6.63-5.37-12-12-12z"/>
+        </svg>
+        Mit GitHub anmelden
+      </button>
+    </div>
 
-    <div class="mt-6 text-center">
+    <div class="text-center">
       <p class="text-sm text-text-secondary">
         Passwort vergessen?
         <button

frontend/src/app/feature/auth/login/login.component.ts

@@ -4,6 +4,7 @@ import { Router } from '@angular/router';
 import { LoginRequest } from '../../../model/auth/LoginRequest';
 import { AuthService } from '@service/auth.service';
 import { CommonModule } from '@angular/common';
+import { environment } from '@environments/environment';
 
 @Component({
   selector: 'app-login',
@@ -65,6 +66,11 @@ export class LoginComponent {
     });
   }
 
+  loginWithGithub(): void {
+    this.isLoading.set(true);
+    window.location.href = `${environment.apiUrl}/oauth2/github/authorize`;
+  }
+
   switchToForgotPassword() {
     this.forgotPassword.emit();
   }

frontend/src/app/feature/auth/oauth2/oauth2-callback.component.ts

@@ -0,0 +1,62 @@
+import { Component, OnInit } from '@angular/core';
+import { CommonModule } from '@angular/common';
+import { ActivatedRoute, Router } from '@angular/router';
+import { AuthService } from '@service/auth.service';
+
+@Component({
+  selector: 'app-oauth2-callback',
+  standalone: true,
+  imports: [CommonModule],
+  template: `
+    <div class="min-h-screen bg-deep-blue flex items-center justify-center">
+      <div class="text-center">
+        <h2 class="text-2xl font-bold text-white mb-4">Finishing authentication...</h2>
+        <div class="animate-spin rounded-full h-12 w-12 border-t-2 border-b-2 border-emerald mx-auto"></div>
+        <p *ngIf="error" class="mt-4 text-accent-red">{{ error }}</p>
+      </div>
+    </div>
+  `,
+})
+export class OAuth2CallbackComponent implements OnInit {
+  error: string | null = null;
+
+  constructor(
+    private route: ActivatedRoute,
+    private router: Router,
+    private authService: AuthService
+  ) {}
+
+  ngOnInit(): void {
+    // Check for code in URL params
+    this.route.queryParams.subscribe(params => {
+      const code = params['code'];
+
+      if (code) {
+        // Exchange GitHub code for a JWT token
+        this.authService.githubAuth(code).subscribe({
+          next: () => {
+            // Redirect to home after successful authentication
+            this.router.navigate(['/home']);
+          },
+          error: (err) => {
+            console.error('GitHub authentication error:', err);
+            this.error = err.error?.message || "Authentication failed. Please try again.";
+            console.log('Error details:', err);
+            
+            // Redirect back to landing page after showing error
+            setTimeout(() => {
+              this.router.navigate(['/']);
+            }, 3000);
+          }
+        });
+      } else {
+        this.error = "Authentication failed. No authorization code received.";
+        
+        // Redirect back to landing page after showing error
+        setTimeout(() => {
+          this.router.navigate(['/']);
+        }, 3000);
+      }
+    });
+  }
+}