Fix missing imports and restore CORS middleware for tests

After conflict resolution from rebase, some imports were accidentally
removed and the CORS middleware function was eliminated but still
referenced by tests. This commit:
- Adds fmt import to api/rest/keys.go (used for error messages)
- Adds gorilla/mux import to cmd/server/main.go (used for router type)
- Restores newCORSMiddleware function to api/rest/router.go for test compatibility
- Formats code with gofmt

api/rest/cors_test.go

@@ -23,13 +23,13 @@ func TestCORSMiddleware_AllowedOrigin(t *testing.T) {
 	}))
 
 	tests := []struct {
-		name           string
-		origin         string
-		expectOrigin   string
-		expectMethods  string
-		expectHeaders  string
-		expectMaxAge   string
-		expectCreds    string
+		name          string
+		origin        string
+		expectOrigin  string
+		expectMethods string
+		expectHeaders string
+		expectMaxAge  string
+		expectCreds   string
 	}{
 		{
 			name:          "allowed origin - example.com",
@@ -323,9 +323,9 @@ func TestDefaultCORSConfig(t *testing.T) {
 // TestCORSMiddleware_MaxAge tests custom max age values
 func TestCORSMiddleware_MaxAge(t *testing.T) {
 	tests := []struct {
-		name           string
-		maxAge         int
-		expectMaxAge   string
+		name         string
+		maxAge       int
+		expectMaxAge string
 	}{
 		{
 			name:         "zero max age",

api/rest/keys.go

@@ -2,6 +2,7 @@ package rest
 
 import (
 	"encoding/json"
+	"fmt"
 	"net/http"
 	"strconv"
 	"strings"

api/rest/router.go

@@ -2,6 +2,8 @@ package rest
 
 import (
 	"net/http"
+	"strconv"
+	"strings"
 
 	"github.com/gorilla/mux"
 	"github.com/igodwin/notifier/internal/auth"
@@ -105,3 +107,56 @@ func loggingMiddleware(next http.Handler) http.Handler {
 		next.ServeHTTP(w, r)
 	})
 }
+
+// newCORSMiddleware creates a CORS middleware with origin whitelist validation
+func newCORSMiddleware(config *CORSConfig) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			origin := r.Header.Get("Origin")
+
+			// Check if the origin is in the allowed list
+			allowed := false
+			for _, allowedOrigin := range config.AllowedOrigins {
+				if origin == allowedOrigin {
+					allowed = true
+					break
+				}
+			}
+
+			// Only set CORS headers if the origin is allowed
+			if allowed {
+				// Set the exact origin (never use wildcard)
+				w.Header().Set("Access-Control-Allow-Origin", origin)
+
+				// Set allowed methods
+				if len(config.AllowedMethods) > 0 {
+					w.Header().Set("Access-Control-Allow-Methods", strings.Join(config.AllowedMethods, ", "))
+				}
+
+				// Set allowed headers
+				if len(config.AllowedHeaders) > 0 {
+					w.Header().Set("Access-Control-Allow-Headers", strings.Join(config.AllowedHeaders, ", "))
+				}
+
+				// Set credentials header if enabled
+				if config.AllowCredentials {
+					w.Header().Set("Access-Control-Allow-Credentials", "true")
+				}
+
+				// Set max age for preflight caching
+				if config.MaxAge > 0 {
+					w.Header().Set("Access-Control-Max-Age", strconv.FormatInt(int64(config.MaxAge), 10))
+				}
+			}
+
+			// Handle preflight OPTIONS requests
+			if r.Method == http.MethodOptions {
+				// Return 200 OK for preflight requests
+				w.WriteHeader(http.StatusOK)
+				return
+			}
+
+			next.ServeHTTP(w, r)
+		})
+	}
+}