Starting with LemonTree 2.5.1, the LemonTree Enterprise Architect Addin uses a regular Git Client for all interactions with the remote repository (Fetch, Push operations).
As such, the authentications methods available to you depend on your local git configuration. Storage and retrieval of credentials is handled by the Git Credential Manager, which in turn utilizes the Windows Credential Manager.
The Enterprise Architect Addin distributed as part of LemonTree 2.5 is limited to an authentication based on username and password, which the user is prompted for directly by the Addin.
The credentials are remembered until you close the Enterprise Architect instance.