added get_actor_user method to data model

[biancafu-panther]

Background

A customer was receiving alerts from the out-of-the-box (OOTB) detection GCP IAM serviceAccounts getAccessToken Privilege Escalation. The alert message included [GCP]: [<ACTOR_NOT_FOUND>] performed [GenerateAccessToken] on project, which indicated that Panther's data model did not recognize the actor correctly.

Upon investigation, we found that the issue arose because the GCP Audit schema in Panther was only mapping the principalEmail field as the actor_user, while for third-party identity callers, GCP populates the principalSubject field instead of principalEmail. This behavior is confirmed by the GCP documentation.

Changes

• Added a method get_actor_user to use principalSubject for actor_user field when principalEmail is not present
• Applied the get_actor_user method to 'username' field since it was also mapping to principalEmail previously
• Modified alert title of GCP IAM serviceAccounts getAccessToken Privilege Escalation to use the actor_user udm field

Testing

• make lint, make test
• added the unit test Principal Subject Used

[github-actions[bot]]

:scream: looks like some things could be wrong with the packs

[INFO][root]: ignoring file dependabot.yml