add util.add_samesite_fields(response, value)

This function adds f"SameSite={value}" to each cookie's header
stored in response.

This is needed because starlette does not currently support
the `samesite` argument in Response.set_cookie. It is merged,
however, and waiting for next release.

Signed-off-by: Kevin Morris <kevr@0cost.org>

test/test_auth_routes.py

@@ -111,6 +111,8 @@ def test_secure_login(mock):
     cookie = next(c for c in response.cookies if c.name == "AURSID")
     assert cookie.secure is True
     assert cookie.has_nonstandard_attr("HttpOnly") is True
+    assert cookie.has_nonstandard_attr("SameSite") is True
+    assert cookie.get_nonstandard_attr("SameSite") == "strict"
     assert cookie.value is not None and len(cookie.value) > 0
 
     # Let's make sure we actually have a session relationship