I've found that one can generate a Personal Access Token to interact with the Bamboo API in place of a username/password, but I have had trouble using my PAT to download logs from previous Bamboo builds.
Via the /rest/api endpoints using Bearer authentication, I can successfully load a resource like so:
https://{host}/rest/api/latest/result/{build-plan}-148?expand=artifacts
And I can list the build artifacts which includes a link to the log I want like so:
https://{host}/download/{build-plan}/build_logs/{build-plan}-148.log
But when I attempt to access the .log resource above using the same Bearer authentication I get an authorization error and it treats me like I am not logged in.
My assumption is that if the log file were available at a /rest/api URL that would have been provided in the list of build artifacts, so I suppose at this point I just want confirmation that using Bearer authentication to get a log file is not supported.