Segfault when using QAbstractOAuth::setModifyParametersFunction

Bryce Beagle bryce.beagle at
Tue May 11 19:21:06 BST 2021

Hi, I'm trying to implement OAuth 2.0 Authorization Code Flow with PKCE in
my PyQt application and am having trouble making use of
QAbstractOAuth::modifyParametersFunction in my QOAuth2AuthorizationCodeFlow

>>> print(self.modifyParametersFunction)
<built-in method modifyParametersFunction of CognitoOAuthFlow object at

>>> print(self.modifyParametersFunction())
SystemError: <built-in method modifyParametersFunction of CognitoOAuthFlow
object at 0x7f8ea0162b80> returned NULL without setting an error

This isn't *too* surprising as this function pointer should be set to NULL
within Qt until QAbstractOAuth::setModifyParametersFunction is called, but
I would expect it to have a more elegant PyQt return value (such as a
Python None), or to throw a more descriptive error.

However, and this is causing my issues, I can't figure out how to actually
use QAbstractOAuth::setModifyParametersFunction properly.

>>> def modifyParamsFunction(stage: QAbstractOAuth.Stage, parameters: dict):
...     if stage is QAbstractOAuth.RequestingAuthorization:
...         parameters["identity_provider"] = "COGNITO"
...         parameters["code_challenge_method"] = "S256"
...         ...  # other stuff
>>> class CognitoOAuthFlow(QOAuth2AuthorizationCodeFlow):
...     def __init__(*args, **kwargs):
...         ...
...         self.setModifyParametersFunction(modifyParamsFunction)

When I try using CognitoOAuthFlow.grant() (after setting up my
URLs/scopes/identifiers/etc.), I get a segfault.

Process finished with exit code 139 (interrupted by signal 11: SIGSEGV)

Is there something I'm missing here? If necessary, I can try to provide a
more complete example, but it might require me to include information about
our authorization flow.

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