Webapp2 Python set_cookie does not support samesite cookie?

Samesite was introduced in webob 1.8 but The App Engine Standard Environment SDK ships with 1.1.1 and 1.2.3 as built-in libraries.

You could try vendoring in a more recent webob to see if this overrides the built-in version.

Once a version of webob that supports samesite is installed, a samesite keyword argument can be passed to Response.set_cookie

class MyHandler(webapp2.RequestHandler):
    def get(self):
        self.response.set_cookie('cookie-name', value='42', samesite='lax')

This sample app sets samesite=strict on the session cookie generated by webapp2_extras.sessions, assuming the underlying webob package supports it.

import webapp2
from webapp2_extras import sessions

class HelloHandler(webapp2.RequestHandler):
    def dispatch(self):
        self.session_store = sessions.get_store(request=self.request)
            super(HelloHandler, self).dispatch()

    def session(self):
        return self.session_store.get_session()

    def get(self):
        self.session['hello'] = 'world'
        self.response.headers['content-type'] = 'text/plain'
        self.response.write('Hello world')

webapp2_config = { 
    'webapp2_extras.sessions': {
        'secret_key': 's3cr3t',
        'cookie_args':{'samesite': 'strict'}

application = webapp2.WSGIApplication([
    webapp2.Route(r'/', handler=HelloHandler),

The response's set-cookie header is

session=eyJoZWxsbyI6IndvcmxkIn0=|1595151290|09b22484901689e6eb0411792c8732ef134d2b66; Path=/; SameSite=strict