Hi @gil,
Agent go configuration explicity talks about API KEY: https://www.elastic.co/guide/en/apm/agent/go/current/configuration.html#config-api-key
Creation of a key at server side creates both an Api Key and Credentials, so it is misleading which of the two should be used (instead, I don't understand when to use one, and when the other):
https://www.elastic.co/guide/en/apm/server/master/api-key.html
Moreover, documentation of API Keys on Elastic doesn't mention Credentials at all:
https://www.elastic.co/guide/en/elasticsearch/reference/current/security-api-get-api-key.html
Finally, I was unable to understand how (if) to set apm-server keys on Elastic, and let them flow to apm-server nodes.
I hope this clarifies better my statement.
I'll open a feature request about recording agent authentication information