#1 add authorization with firebase

Co-authored-by: Tim <timwundenberg@outlook.de>
Reviewed-on: tim/me-fit#2

api/utils/auth.go

@@ -0,0 +1,36 @@
+package utils
+
+import (
+	"context"
+	"log"
+
+	firebase "firebase.google.com/go"
+	"firebase.google.com/go/auth"
+	"google.golang.org/api/option"
+)
+
+var app *firebase.App
+
+func VerifyToken(token string) (*auth.Token, error) {
+	if app == nil {
+		setup()
+	}
+
+	client, err := app.Auth(context.Background())
+	if err != nil {
+		log.Fatalf("error getting Auth client: %v\n", err)
+	}
+	return client.VerifyIDToken(context.Background(), token)
+}
+
+func setup() {
+	opt := option.WithCredentialsFile("./secrets/me-fit-a9365-firebase-adminsdk-8065w-7cf8443902.json")
+
+	firebaseApp, err := firebase.NewApp(context.Background(), nil, opt)
+
+	if err != nil {
+		log.Fatalf("error initializing app: %v", err)
+	}
+
+	app = firebaseApp
+}