When authentication is turned on in your GoCD Server setup, add the --user option to the curl command, like this:
Each pipeline in the pipeline activity page can now be annotated with a comment. This text can be seen by all other users who can access this page, for those pipelines.
When this feature is turned on, the pipeline activity page looks like this:
Clicking on the "Add Comment" button for a pipeline run brings up a text box for you to enter some text. It looks like this:
Once you click "Submit", after entering some text, that text shows up against the pipeline run, like so: