Problem

After upgrading Git Integration Plugin for JIRA add-on to version 2.6.13+ it is not possible to login in JIRA.

Workaround

 Downgrade the Git Integration Plugin for JIRA to a version earlier than 2.6.13.

1. Stop JIRA
2. Download the earlier plugin version
3. Remove the upgraded version from both installed-plugins and .osgi-plugins
4. Add the earlier version in both of the above cited folders
5. Update the plugin version at the column pluginversion in the table pluginversion
6. Start JIRA

Resolution

 This bug has been fixed in version 2.6.17.