Logging into SO using a Google account is just authenticating a user using OAuth and is a different topic. A typical scenario for using SCIM is you get hired at a company and as part of onboarding, the company’s Okta tenant sends a SCIM request to automatically create an account for you in their corporate Stack Overflow tenant. As part of your SO profile creation, Okta can include an optional Okta-specific identifier which is how Okta distinguishes you from everyone else. This is the external ID. Why’s this field useful? Well it’s one way that Okta can quickly find your account in SO in the future to make profile updates like updating a job title profile field.