When doing a ruby gem push, it fails because authentication is not available:

gem push <gem file> --host http://<redacted>/rubygems/RubyGem

When trying to set the credentials file (~/.gem/credentials), it fails with an Endpoint Not Found error

curl http://<redacted>/rubygems/RubyGem -u user > ~/.gem/credentials

How to we get around this to push the gems to the server?

Edit: I manually created the file, but this error is still not expected.