Retrieve a specific signature enrollment.

Retrieve a specific enrollment of a signature authentication method.

Entitlements:
- manageEnrollMFAMethodAnyUser (Manage second-factor authentication enrollment for all users)
- manageEnrollMFAMethod (Manage own second-factor authentication enrollment)
- readEnrollMFAMethodAnyUser (Read second-factor authentication enrollment for all users)
- readEnrollMFAMethod (Read own second-factor authentication enrollment)
- verifyAuthenticator (Use IBM Verify)