We are using the 'Specify SCM login/password' functionality in our release builds. The plugin configuration currently allows to preselect the fields for a custom SCM comment prefix, but it's not possible to preselect the SCM credential fields.

A further idea would be to set the current Jenkins user as the default SCM user name. Do you think that this would be possible as it's not always guaranteed that these two user names are equal (depending on the underlying authentication configuration)?