[X-Istence]

Github will happily hand you an access token by visiting "https://github.com/settings/tokens".

These are bearer tokens, in that the bearer gets granted access by that token alone.

You happen to send it along in a Basic authentication in HTTP instead of as an Authorization header, but it is a bearer token all the same.

No OAuth2 flow required.

[X-Istence]

Any service that uses API keys are basically handing out bearer tokens. Whoever holds that API key can make requests to the service, it grants you access.