Green Button Alliance Authentication
Three distinct authentication surfaces sit under the Green Button Alliance name and must not be conflated. (1) The CMD ESPI resource server contract - OAuth 2.0 authorization_code and client_credentials, bearer tokens, ESPI Function Block scope grammar; this is the interface every certified Data Custodian implements, not a service GBA runs. (2) The OpenESPI Authorization Server GBA publishes as a reference implementation - JWT bearer, HTTP basic client credentials, and X.509 mutual TLS client certificates, TLS 1.3 only. (3) GBA's own member single sign-on - a standard OIDC provider for the association's membership system, which grants no access to any energy data at all.
Green Button Alliance secures its APIs with http, mutualTLS, oauth2, and openIdConnect across 4 declared security schemes, as derived from its OpenAPI definitions. OAuth 2.0 is offered via the authorizationCode, clientCredentials, and refreshToken flow(s).