All routing logic in app.py are working correctly.

frontend/app.py

@@ -2,9 +2,16 @@ from flask import Flask, request, render_template, url_for, redirect
 
 app = Flask(__name__)
 
-@app.route("/")
+@app.route("/", methods=['GET', 'POST'])
 def groclist_home():
-	return render_template('index.html')
+	error = None
+	if request.method == 'POST':
+		if request.form.get('login') == 'Inloggen':
+			return redirect(url_for('groclist_login'))
+	elif request.method == 'GET':
+		return render_template('index.html')
+
+	return render_template('index.html',error=error)
 
 @app.route("/welcome")
 def groclist_welcome():
@@ -20,6 +27,9 @@ def groclist_login():
 			return redirect(url_for('groclist_welcome'))
 	return render_template("login.html", error=error)
 
+
+app.add_url_rule("/welcome", "welcome", groclist_welcome)  
+
 # start server with run method
 if __name__ == "__main__":
 	app.run(debug=True)

frontend/templates/index.html

@@ -11,4 +11,7 @@
     <p class="important">
       Welkom bij Groclist
     </p>
+    <form method="post" action="/">
+        <input type="submit" value="Inloggen" name="login"/>
+    </form>
 {% endblock %}