Relic does not manage passwords itself; sign-in is handled through Suite single sign-on. The externalId is the link that makes this work: it stores the identifier Suite uses for the person, so when they log in, Relic can match the incoming identity to the right local User record. It must be unique, which guarantees that one Suite identity maps to exactly one Relic user and prevents duplicate accounts for the same person. You generally do not edit this by hand — it is set when the user is first provisioned from Suite. It works alongside email and name, which carry the user's readable contact details.
Technical section
Data model, API, and internals — visible to developers.