Changes where made in https://github.com/mattermost/mattermost-plugin-github/pull/166 to support the plugin working when ExperimentalStrictCSRFEnforcement is set to true.
When the flag is true the Attach to GitHub Issue functionality does not work. The user will see an error about being unauthorized in the modal and the web request returns a 401 response.
Install and configure GitHub plugin
Set ExperimentalStrictCSRFEnforcement to True
Click the "..." on a post and select Attach to GitHub Issue
Select an issue using the search and click Attach
Observed: User will see an error about being unauthorized