Update: The hung process apparently terminated (with feedback) sometime overnight:
I’m still looking into possibilities, but if this looks familiar to anyone, please do share.
The SatisPress server to which this composer_authentications config is attempting to connect does indeed work well with other projects, including this very project: I’m getting this error when attempting to provision development, but I can deploy to one of the project’s previously provisioned remotes (and I have verified that composer dependencies are indeed installed on the remote every time).