feat: Enhance OAuth2 support with multi-application configuration and CORS middleware

- Introduced support for multiple applications using the same OAuth endpoints with different redirect URIs.
- Added environment variable configurations for allowed redirect domains and default redirect URIs.
- Implemented CORS middleware to manage cross-origin requests based on the environment.
- Updated OAuth2 handlers to securely manage redirect URIs and state parameters, improving security against open redirect vulnerabilities.
- Enhanced API documentation to reflect new multi-application OAuth configuration and usage examples.

Author: gjovanovicst

cmd/api/main.go

@@ -82,6 +82,9 @@ func main() {
 	// Setup Gin Router
 	r := gin.Default()
 
+	// Add CORS middleware
+	r.Use(middleware.CORSMiddleware())
+
 	// Public routes
 	public := r.Group("/")
 	{

docs/multi-app-oauth-config.md

@@ -0,0 +1,159 @@
+# Multi-Application OAuth Configuration
+
+## Overview
+The authentication API now supports multiple applications using the same OAuth endpoints with different redirect URIs. This allows you to have multiple frontends (e.g., admin panel, user portal, mobile app) that all use the same authentication backend.
+
+## Configuration
+
+### Environment Variables
+
+Add these variables to your `.env` file:
+
+```env
+# Multi-Application Support
+# Comma-separated list of allowed redirect domains for OAuth callbacks
+ALLOWED_REDIRECT_DOMAINS=localhost:3000,localhost:5173,localhost:8080,example.com,.example.com
+
+# Default redirect URI when none is specified
+DEFAULT_REDIRECT_URI=http://localhost:5173/auth/callback
+
+# Production frontend URL for CORS
+FRONTEND_URL=https://your-production-domain.com
+```
+
+### Domain Configuration
+
+#### Development
+For local development, include all your local ports:
+```env
+ALLOWED_REDIRECT_DOMAINS=localhost:3000,localhost:5173,localhost:8080,127.0.0.1:3000,127.0.0.1:5173
+```
+
+#### Production
+For production, specify your allowed domains:
+```env
+# Allow specific domains
+ALLOWED_REDIRECT_DOMAINS=myapp.com,admin.myapp.com
+
+# Allow all subdomains with dot notation
+ALLOWED_REDIRECT_DOMAINS=.myapp.com,anotherapp.com
+```
+
+## Usage
+
+### Frontend Integration
+
+#### 1. Basic Usage (Default Redirect)
+```javascript
+// Will redirect to DEFAULT_REDIRECT_URI after OAuth
+window.location.href = '/auth/google/login';
+```
+
+#### 2. Custom Redirect URI
+```javascript
+// Will redirect to specified URI after OAuth
+const redirectUri = 'https://admin.myapp.com/auth/callback';
+window.location.href = `/auth/google/login?redirect_uri=${encodeURIComponent(redirectUri)}`;
+```
+
+#### 3. Handling Callbacks
+Your frontend should handle the callback URL parameters:
+
+```javascript
+// In your /auth/callback route
+const urlParams = new URLSearchParams(window.location.search);
+
+if (urlParams.get('error')) {
+  // Handle error
+  console.error('OAuth error:', urlParams.get('error'));
+} else if (urlParams.get('access_token')) {
+  // Handle success
+  const accessToken = urlParams.get('access_token');
+  const refreshToken = urlParams.get('refresh_token');
+  const provider = urlParams.get('provider'); // 'google', 'facebook', or 'github'
+  
+  // Store tokens and redirect to app
+  localStorage.setItem('access_token', accessToken);
+  localStorage.setItem('refresh_token', refreshToken);
+  window.location.href = '/dashboard';
+}
+```
+
+### API Endpoints
+
+All OAuth providers support the same pattern:
+
+- **Google**: 
+  - Login: `GET /auth/google/login?redirect_uri=...`
+  - Callback: `GET /auth/google/callback`
+
+- **Facebook**: 
+  - Login: `GET /auth/facebook/login?redirect_uri=...`
+  - Callback: `GET /auth/facebook/callback`
+
+- **GitHub**: 
+  - Login: `GET /auth/github/login?redirect_uri=...`
+  - Callback: `GET /auth/github/callback`
+
+## Security Features
+
+### 1. Domain Whitelist
+- Only domains in `ALLOWED_REDIRECT_DOMAINS` are accepted
+- Prevents open redirect vulnerabilities
+- Supports subdomain wildcards with dot notation
+
+### 2. Secure State Management
+- OAuth state parameter contains encrypted redirect URI
+- Includes timestamp to prevent replay attacks
+- Cryptographically secure random nonce generation
+
+### 3. CORS Configuration
+- Automatic CORS headers for allowed domains
+- Supports credentials for secure cookie handling
+- Production-ready with configurable origins
+
+## Examples
+
+### Multi-Domain Setup
+```env
+# Support multiple applications
+ALLOWED_REDIRECT_DOMAINS=app.mycompany.com,admin.mycompany.com,mobile.mycompany.com
+DEFAULT_REDIRECT_URI=https://app.mycompany.com/auth/callback
+```
+
+### Development Setup
+```env
+# Support local development
+ALLOWED_REDIRECT_DOMAINS=localhost:3000,localhost:5173,localhost:8080
+DEFAULT_REDIRECT_URI=http://localhost:5173/auth/callback
+```
+
+### Production with Subdomains
+```env
+# Allow all subdomains of mycompany.com
+ALLOWED_REDIRECT_DOMAINS=.mycompany.com,mycompany.com
+DEFAULT_REDIRECT_URI=https://mycompany.com/auth/callback
+```
+
+## Error Handling
+
+The API will redirect to the frontend with error parameters:
+
+- `?error=invalid_state` - Invalid or expired OAuth state
+- `?error=authorization_code_missing` - OAuth provider didn't return code
+- `?error=missing_state` - OAuth state parameter missing
+- `?error=Invalid%20redirect%20URI` - Redirect URI not in whitelist
+
+## Migration Guide
+
+### From Single Application
+If you were using the hardcoded redirect URI:
+
+1. Add the environment variables to your `.env` file
+2. Your existing setup will continue to work with default values
+3. Optionally, start using the `redirect_uri` parameter for flexibility
+
+### For New Applications
+1. Set up the environment variables
+2. Add your domain to `ALLOWED_REDIRECT_DOMAINS`
+3. Use the `redirect_uri` parameter in your OAuth login URLs 

go.mod

@@ -27,15 +27,16 @@ require (
 	filippo.io/edwards25519 v1.1.0 // indirect
 	github.com/KyleBanks/depth v1.2.1 // indirect
 	github.com/boombuler/barcode v1.0.1-0.20190219062509-6c824513bacc // indirect
-	github.com/bytedance/sonic v1.11.6 // indirect
-	github.com/bytedance/sonic/loader v0.1.1 // indirect
+	github.com/bytedance/sonic v1.13.3 // indirect
+	github.com/bytedance/sonic/loader v0.2.4 // indirect
 	github.com/cespare/xxhash/v2 v2.3.0 // indirect
-	github.com/cloudwego/base64x v0.1.4 // indirect
+	github.com/cloudwego/base64x v0.1.5 // indirect
 	github.com/cloudwego/iasm v0.2.0 // indirect
 	github.com/dgryski/go-rendezvous v0.0.0-20200823014737-9f7001d12a5f // indirect
 	github.com/fsnotify/fsnotify v1.8.0 // indirect
-	github.com/gabriel-vasile/mimetype v1.4.8 // indirect
-	github.com/gin-contrib/sse v0.1.0 // indirect
+	github.com/gabriel-vasile/mimetype v1.4.9 // indirect
+	github.com/gin-contrib/cors v1.7.6 // indirect
+	github.com/gin-contrib/sse v1.1.0 // indirect
 	github.com/go-openapi/jsonpointer v0.21.1 // indirect
 	github.com/go-openapi/jsonreference v0.21.0 // indirect
 	github.com/go-openapi/spec v0.21.0 // indirect
@@ -44,7 +45,7 @@ require (
 	github.com/go-playground/universal-translator v0.18.1 // indirect
 	github.com/go-sql-driver/mysql v1.8.1 // indirect
 	github.com/go-viper/mapstructure/v2 v2.2.1 // indirect
-	github.com/goccy/go-json v0.10.2 // indirect
+	github.com/goccy/go-json v0.10.5 // indirect
 	github.com/jackc/pgpassfile v1.0.0 // indirect
 	github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 // indirect
 	github.com/jackc/pgx/v5 v5.6.0 // indirect
@@ -53,13 +54,13 @@ require (
 	github.com/jinzhu/now v1.1.5 // indirect
 	github.com/josharian/intern v1.0.0 // indirect
 	github.com/json-iterator/go v1.1.12 // indirect
-	github.com/klauspost/cpuid/v2 v2.2.7 // indirect
+	github.com/klauspost/cpuid/v2 v2.2.10 // indirect
 	github.com/leodido/go-urn v1.4.0 // indirect
 	github.com/mailru/easyjson v0.9.0 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
 	github.com/modern-go/reflect2 v1.0.2 // indirect
-	github.com/pelletier/go-toml/v2 v2.2.3 // indirect
+	github.com/pelletier/go-toml/v2 v2.2.4 // indirect
 	github.com/pquerna/otp v1.5.0 // indirect
 	github.com/sagikazarmark/locafero v0.7.0 // indirect
 	github.com/skip2/go-qrcode v0.0.0-20200617195104-da1b6568686e // indirect
@@ -69,16 +70,16 @@ require (
 	github.com/spf13/pflag v1.0.6 // indirect
 	github.com/subosito/gotenv v1.6.0 // indirect
 	github.com/twitchyliquid64/golang-asm v0.15.1 // indirect
-	github.com/ugorji/go/codec v1.2.12 // indirect
+	github.com/ugorji/go/codec v1.3.0 // indirect
 	go.uber.org/atomic v1.9.0 // indirect
 	go.uber.org/multierr v1.9.0 // indirect
-	golang.org/x/arch v0.8.0 // indirect
+	golang.org/x/arch v0.18.0 // indirect
 	golang.org/x/net v0.41.0 // indirect
 	golang.org/x/sync v0.15.0 // indirect
 	golang.org/x/sys v0.33.0 // indirect
 	golang.org/x/text v0.26.0 // indirect
 	golang.org/x/tools v0.34.0 // indirect
-	google.golang.org/protobuf v1.36.1 // indirect
+	google.golang.org/protobuf v1.36.6 // indirect
 	gopkg.in/alexcesaro/quotedprintable.v3 v3.0.0-20150716171945-2caba252f4dc // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 	gorm.io/datatypes v1.2.5 // indirect

go.sum

@@ -8,12 +8,18 @@ github.com/boombuler/barcode v1.0.1-0.20190219062509-6c824513bacc h1:biVzkmvwrH8
 github.com/boombuler/barcode v1.0.1-0.20190219062509-6c824513bacc/go.mod h1:paBWMcWSl3LHKBqUq+rly7CNSldXjb2rDl3JlRe0mD8=
 github.com/bytedance/sonic v1.11.6 h1:oUp34TzMlL+OY1OUWxHqsdkgC/Zfc85zGqw9siXjrc0=
 github.com/bytedance/sonic v1.11.6/go.mod h1:LysEHSvpvDySVdC2f87zGWf6CIKJcAvqab1ZaiQtds4=
+github.com/bytedance/sonic v1.13.3 h1:MS8gmaH16Gtirygw7jV91pDCN33NyMrPbN7qiYhEsF0=
+github.com/bytedance/sonic v1.13.3/go.mod h1:o68xyaF9u2gvVBuGHPlUVCy+ZfmNNO5ETf1+KgkJhz4=
 github.com/bytedance/sonic/loader v0.1.1 h1:c+e5Pt1k/cy5wMveRDyk2X4B9hF4g7an8N3zCYjJFNM=
 github.com/bytedance/sonic/loader v0.1.1/go.mod h1:ncP89zfokxS5LZrJxl5z0UJcsk4M4yY2JpfqGeCtNLU=
+github.com/bytedance/sonic/loader v0.2.4 h1:ZWCw4stuXUsn1/+zQDqeE7JKP+QO47tz7QCNan80NzY=
+github.com/bytedance/sonic/loader v0.2.4/go.mod h1:N8A3vUdtUebEY2/VQC0MyhYeKUFosQU6FxH2JmUe6VI=
 github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
 github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
 github.com/cloudwego/base64x v0.1.4 h1:jwCgWpFanWmN8xoIUHa2rtzmkd5J2plF/dnLS6Xd/0Y=
 github.com/cloudwego/base64x v0.1.4/go.mod h1:0zlkT4Wn5C6NdauXdJRhSKRlJvmclQ1hhJgA0rcu/8w=
+github.com/cloudwego/base64x v0.1.5 h1:XPciSp1xaq2VCSt6lF0phncD4koWyULpl5bUxbfCyP4=
+github.com/cloudwego/base64x v0.1.5/go.mod h1:0zlkT4Wn5C6NdauXdJRhSKRlJvmclQ1hhJgA0rcu/8w=
 github.com/cloudwego/iasm v0.2.0 h1:1KNIy1I1H9hNNFEEH3DVnI4UujN+1zjpuk6gwHLTssg=
 github.com/cloudwego/iasm v0.2.0/go.mod h1:8rXZaNYT2n95jn+zTI1sDr+IgcD2GVs0nlbbQPiEFhY=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
@@ -27,10 +33,16 @@ github.com/fsnotify/fsnotify v1.8.0 h1:dAwr6QBTBZIkG8roQaJjGof0pp0EeF+tNV7YBP3F/
 github.com/fsnotify/fsnotify v1.8.0/go.mod h1:8jBTzvmWwFyi3Pb8djgCCO5IBqzKJ/Jwo8TRcHyHii0=
 github.com/gabriel-vasile/mimetype v1.4.8 h1:FfZ3gj38NjllZIeJAmMhr+qKL8Wu+nOoI3GqacKw1NM=
 github.com/gabriel-vasile/mimetype v1.4.8/go.mod h1:ByKUIKGjh1ODkGM1asKUbQZOLGrPjydw3hYPU2YU9t8=
+github.com/gabriel-vasile/mimetype v1.4.9 h1:5k+WDwEsD9eTLL8Tz3L0VnmVh9QxGjRmjBvAG7U/oYY=
+github.com/gabriel-vasile/mimetype v1.4.9/go.mod h1:WnSQhFKJuBlRyLiKohA/2DtIlPFAbguNaG7QCHcyGok=
+github.com/gin-contrib/cors v1.7.6 h1:3gQ8GMzs1Ylpf70y8bMw4fVpycXIeX1ZemuSQIsnQQY=
+github.com/gin-contrib/cors v1.7.6/go.mod h1:Ulcl+xN4jel9t1Ry8vqph23a60FwH9xVLd+3ykmTjOk=
 github.com/gin-contrib/gzip v0.0.6 h1:NjcunTcGAj5CO1gn4N8jHOSIeRFHIbn51z6K+xaN4d4=
 github.com/gin-contrib/gzip v0.0.6/go.mod h1:QOJlmV2xmayAjkNS2Y8NQsMneuRShOU/kjovCXNuzzk=
 github.com/gin-contrib/sse v0.1.0 h1:Y/yl/+YNO8GZSjAhjMsSuLt29uWRFHdHYUb5lYOV9qE=
 github.com/gin-contrib/sse v0.1.0/go.mod h1:RHrZQHXnP2xjPF+u1gW/2HnVO7nvIa9PG3Gm+fLHvGI=
+github.com/gin-contrib/sse v1.1.0 h1:n0w2GMuUpWDVp7qSpvze6fAu9iRxJY4Hmj6AmBOU05w=
+github.com/gin-contrib/sse v1.1.0/go.mod h1:hxRZ5gVpWMT7Z0B0gSNYqqsSCNIJMjzvm6fqCz9vjwM=
 github.com/gin-gonic/gin v1.10.1 h1:T0ujvqyCSqRopADpgPgiTT63DUQVSfojyME59Ei63pQ=
 github.com/gin-gonic/gin v1.10.1/go.mod h1:4PMNQiOhvDRa013RKVbsiNwoyezlm2rm0uX/T7kzp5Y=
 github.com/go-openapi/jsonpointer v0.21.1 h1:whnzv/pNXtK2FbX/W9yJfRmE2gsmkfahjMKB0fZvcic=
@@ -58,6 +70,8 @@ github.com/go-viper/mapstructure/v2 v2.2.1 h1:ZAaOCxANMuZx5RCeg0mBdEZk7DZasvvZIx
 github.com/go-viper/mapstructure/v2 v2.2.1/go.mod h1:oJDH3BJKyqBA2TXFhDsKDGDTlndYOZ6rGS0BRZIxGhM=
 github.com/goccy/go-json v0.10.2 h1:CrxCmQqYDkv1z7lO7Wbh2HN93uovUHgrECaO5ZrCXAU=
 github.com/goccy/go-json v0.10.2/go.mod h1:6MelG93GURQebXPDq3khkgXZkazVtN9CRI+MGFi0w8I=
+github.com/goccy/go-json v0.10.5 h1:Fq85nIqj+gXn/S5ahsiTlK3TmC85qgirsdTP/+DeaC4=
+github.com/goccy/go-json v0.10.5/go.mod h1:oq7eo15ShAhp70Anwd5lgX2pLfOS3QCiwU/PULtXL6M=
 github.com/golang-jwt/jwt/v5 v5.2.2 h1:Rl4B7itRWVtYIHFrSNd7vhTiz9UpLdi6gZhZ3wEeDy8=
 github.com/golang-jwt/jwt/v5 v5.2.2/go.mod h1:pqrtFR0X4osieyHYxtmOUWsAWrfe1Q5UVIyoH402zdk=
 github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
@@ -86,6 +100,8 @@ github.com/json-iterator/go v1.1.12/go.mod h1:e30LSqwooZae/UwlEbR2852Gd8hjQvJoHm
 github.com/klauspost/cpuid/v2 v2.0.9/go.mod h1:FInQzS24/EEf25PyTYn52gqo7WaD8xa0213Md/qVLRg=
 github.com/klauspost/cpuid/v2 v2.2.7 h1:ZWSB3igEs+d0qvnxR/ZBzXVmxkgt8DdzP6m9pfuVLDM=
 github.com/klauspost/cpuid/v2 v2.2.7/go.mod h1:Lcz8mBdAVJIBVzewtcLocK12l3Y+JytZYpaMropDUws=
+github.com/klauspost/cpuid/v2 v2.2.10 h1:tBs3QSyvjDyFTq3uoc/9xFpCuOsJQFNPiAhYdw2skhE=
+github.com/klauspost/cpuid/v2 v2.2.10/go.mod h1:hqwkgyIinND0mEev00jJYCxPNVRVXFQeu1XKlok6oO0=
 github.com/knz/go-libedit v1.10.1/go.mod h1:MZTVkCWyz0oBc7JOWP3wNAzd002ZbM/5hgShxwh4x8M=
 github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
 github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=
@@ -110,6 +126,8 @@ github.com/onsi/gomega v1.18.1 h1:M1GfJqGRrBrrGGsbxzV5dqM2U2ApXefZCQpkukxYRLE=
 github.com/onsi/gomega v1.18.1/go.mod h1:0q+aL8jAiMXy9hbwj2mr5GziHiwhAIQpFmmtT5hitRs=
 github.com/pelletier/go-toml/v2 v2.2.3 h1:YmeHyLY8mFWbdkNWwpr+qIL2bEqT0o95WSdkNHvL12M=
 github.com/pelletier/go-toml/v2 v2.2.3/go.mod h1:MfCQTFTvCcUyyvvwm1+G6H/jORL20Xlb6rzQu9GuUkc=
+github.com/pelletier/go-toml/v2 v2.2.4 h1:mye9XuhQ6gvn5h28+VilKrrPoQVanw5PMw/TB0t5Ec4=
+github.com/pelletier/go-toml/v2 v2.2.4/go.mod h1:2gIqNv+qfxSVS7cM2xJQKtLSTLUE9V8t9Stt+h56mCY=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/pquerna/otp v1.5.0 h1:NMMR+WrmaqXU4EzdGJEE1aUUI0AMRzsp96fFFWNPwxs=
@@ -152,6 +170,8 @@ github.com/twitchyliquid64/golang-asm v0.15.1 h1:SU5vSMR7hnwNxj24w34ZyCi/FmDZTkS
 github.com/twitchyliquid64/golang-asm v0.15.1/go.mod h1:a1lVb/DtPvCB8fslRZhAngC2+aY1QWCk3Cedj/Gdt08=
 github.com/ugorji/go/codec v1.2.12 h1:9LC83zGrHhuUA9l16C9AHXAqEV/2wBQ4nkvumAE65EE=
 github.com/ugorji/go/codec v1.2.12/go.mod h1:UNopzCgEMSXjBc6AOMqYvWC1ktqTAfzJZUZgYf6w6lg=
+github.com/ugorji/go/codec v1.3.0 h1:Qd2W2sQawAfG8XSvzwhBeoGq71zXOC/Q1E9y/wUcsUA=
+github.com/ugorji/go/codec v1.3.0/go.mod h1:pRBVtBSKl77K30Bv8R2P+cLSGaTtex6fsA2Wjqmfxj4=
 github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
 go.uber.org/atomic v1.9.0 h1:ECmE8Bn/WFTYwEW/bpKD3M8VtR/zQVbavAoalC1PYyE=
 go.uber.org/atomic v1.9.0/go.mod h1:fEN4uk6kAWBTFdckzkM89CLk9XfWZrxpCo0nPH17wJc=
@@ -160,6 +180,8 @@ go.uber.org/multierr v1.9.0/go.mod h1:X2jQV1h+kxSjClGpnseKVIxpmcjrj7MNnI0bnlfKTV
 golang.org/x/arch v0.0.0-20210923205945-b76863e36670/go.mod h1:5om86z9Hs0C8fWVUuoMHwpExlXzs5Tkyp9hOrfG7pp8=
 golang.org/x/arch v0.8.0 h1:3wRIsP3pM4yUptoR96otTUOXI367OS0+c9eeRi9doIc=
 golang.org/x/arch v0.8.0/go.mod h1:FEVrYAQjsQXMVJ1nsMoVVXPZg6p2JE2mx8psSWTDQys=
+golang.org/x/arch v0.18.0 h1:WN9poc33zL4AzGxqf8VtpKUnGvMi8O9lhNyBMF/85qc=
+golang.org/x/arch v0.18.0/go.mod h1:bdwinDaKcfZUGpH09BB7ZmOfhalA8lQdzl62l8gGWsk=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
 golang.org/x/crypto v0.39.0 h1:SHs+kF4LP+f+p14esP5jAoDpHU8Gu/v9lFRK6IT5imM=
@@ -205,6 +227,8 @@ golang.org/x/tools v0.34.0/go.mod h1:pAP9OwEaY1CAW3HOmg3hLZC5Z0CCmzjAF2UQMSqNARg
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 google.golang.org/protobuf v1.36.1 h1:yBPeRvTftaleIgM3PZ/WBIZ7XM/eEYAaEyCwvyjq/gk=
 google.golang.org/protobuf v1.36.1/go.mod h1:9fA7Ob0pmnwhb644+1+CVWFRbNajQ6iRojtC/QF5bRE=
+google.golang.org/protobuf v1.36.6 h1:z1NpPI8ku2WgiWnf+t9wTPsn6eP1L7ksHUlkfLvd9xY=
+google.golang.org/protobuf v1.36.6/go.mod h1:jduwjTPXsFjZGTmRluh+L6NjiWu7pchiJ2/5YcXBHnY=
 gopkg.in/alexcesaro/quotedprintable.v3 v3.0.0-20150716171945-2caba252f4dc h1:2gGKlE2+asNV9m7xrywl36YYNnBG5ZQ0r/BOOxqPpmk=
 gopkg.in/alexcesaro/quotedprintable.v3 v3.0.0-20150716171945-2caba252f4dc/go.mod h1:m7x9LTH6d71AHyAX77c9yqWCCa3UKHcVEj9y7hAtKDk=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=

internal/middleware/cors.go

@@ -0,0 +1,66 @@
+package middleware
+
+import (
+	"time"
+
+	"github.com/gin-contrib/cors"
+	"github.com/gin-gonic/gin"
+	"github.com/spf13/viper"
+)
+
+// CORSMiddleware creates and configures CORS middleware
+func CORSMiddleware() gin.HandlerFunc {
+	config := cors.Config{
+		AllowOrigins: []string{
+			"http://localhost:3000",       // React dev server
+			"http://localhost:5173",       // Vite dev server
+			"http://localhost:8080",       // API server itself
+			"https://accounts.google.com", // Google OAuth
+			"https://www.facebook.com",    // Facebook OAuth
+			"https://github.com",          // GitHub OAuth
+		},
+		AllowMethods: []string{
+			"GET",
+			"POST",
+			"PUT",
+			"DELETE",
+			"OPTIONS",
+			"HEAD",
+		},
+		AllowHeaders: []string{
+			"Origin",
+			"Content-Type",
+			"Content-Length",
+			"Accept-Encoding",
+			"X-CSRF-Token",
+			"Authorization",
+			"Accept",
+			"Cache-Control",
+			"X-Requested-With",
+		},
+		ExposeHeaders: []string{
+			"Content-Length",
+			"Access-Control-Allow-Origin",
+			"Access-Control-Allow-Headers",
+			"Content-Type",
+		},
+		AllowCredentials: true,
+		MaxAge:           12 * time.Hour,
+	}
+
+	// In production, restrict origins to specific domains
+	if viper.GetString("GIN_MODE") == "release" {
+		// Get frontend URLs from environment
+		frontendURL := viper.GetString("FRONTEND_URL")
+		if frontendURL != "" {
+			config.AllowOrigins = []string{
+				frontendURL,
+				"https://accounts.google.com",
+				"https://www.facebook.com",
+				"https://github.com",
+			}
+		}
+	}
+
+	return cors.New(config)
+}