python Google App Engine : Webapp2 : Authentication

Question

i am using custom user accounts for one of my projects and am using the User model and authentication provided by webapp2. Everything runs perfect but i am stuck at the part where authentication is not successful. For Example: ``` #imports from webapp2_extras.appengine.auth.models import User class LoginHandler(SomeBaseRequestHandler): def get(self): '''self code goes in here''' def post(self): auth_id = 'authentication:id' password = 'somepassword' user = User.get_by_auth_password(authid, password) if user: # code to set a session and redirect to homepage else: # append error list and render a template ``` I am able to login the user however the problem arises if a user provides a wrong user name or password. if the user provides any of the wrong credentials it raises a server side error. ``` Traceback (most recent call last): File "/opt/google_appengine_1.6.4/lib/webapp2/webapp2.py", line 1536, in __call__ rv = self.handle_exception(request, response, e) File "/opt/google_appengine_…

Accepted Answer

You can use try / except to control your login flow:

```
def post(self):
  """
  username: Get the username from POST dict
  password: Get the password from POST dict
  """
  username = self.request.POST.get('username')
  password = self.request.POST.get('password')
  # Try to login user with password
  # Raises InvalidAuthIdError if user is not found
  # Raises InvalidPasswordError if provided password doesn't match with specified user
  try:
    self.auth.get_user_by_password(username, password)
    self.redirect('/secure')
  except (InvalidAuthIdError, InvalidPasswordError), e:
    # Returns error message to self.response.write in the BaseHandler.dispatcher
    # Currently no message is attached to the exceptions
    return e
```

python Google App Engine : Webapp2 : Authentication

Solution

Problem