Add Google Sign-In with templated HTML and env config

main.go

@@ -1,13 +1,97 @@
 package main
 
 import (
+	"bufio"
+	"context"
+	"encoding/json"
+	"html/template"
 	"log"
 	"net/http"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"google.golang.org/api/idtoken"
 )
 
+var (
+	env       = map[string]string{}
+	templates *template.Template
+)
+
+func init() {
+	f, err := os.Open("secrets.env")
+	if err != nil {
+		log.Fatal("[ERROR] failed to open secrets.env: ", err)
+	}
+	defer f.Close()
+
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		line := scanner.Text()
+		if parts := strings.SplitN(line, "=", 2); len(parts) == 2 {
+			env[parts[0]] = parts[1]
+		}
+	}
+
+	templates = template.Must(template.ParseGlob("static/*.html"))
+}
+
 func main() {
-	http.Handle("/", http.FileServer(http.Dir("static")))
+	http.HandleFunc("/", handleStatic)
+	http.HandleFunc("/auth/google/callback", handleGoogleCallback)
 
 	log.Println("server starting on :8080")
 	log.Fatal(http.ListenAndServe(":8080", nil))
 }
+
+func handleStatic(w http.ResponseWriter, r *http.Request) {
+	path := r.URL.Path
+	if path == "/" {
+		path = "/index.html"
+	}
+
+	name := strings.TrimPrefix(path, "/")
+
+	if strings.HasSuffix(name, ".html") {
+		t := templates.Lookup(name)
+		if t == nil {
+			http.NotFound(w, r)
+			return
+		}
+		w.Header().Set("Content-Type", "text/html")
+		t.Execute(w, env)
+		return
+	}
+
+	http.ServeFile(w, r, filepath.Join("static", name))
+}
+
+func handleGoogleCallback(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+
+	credential := r.FormValue("credential")
+	if credential == "" {
+		http.Error(w, "missing credential", http.StatusBadRequest)
+		return
+	}
+
+	payload, err := idtoken.Validate(context.Background(), credential, env["GOOGLE_CLIENT_ID"])
+	if err != nil {
+		log.Println("[ERROR] failed to validate token:", err)
+		http.Error(w, "invalid token", http.StatusUnauthorized)
+		return
+	}
+
+	response := map[string]any{
+		"email":   payload.Claims["email"],
+		"name":    payload.Claims["name"],
+		"picture": payload.Claims["picture"],
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(response)
+}