Secret values in credentials.client_id / client_secret may be $ENV:VAR
references — they are resolved here at exchange time. Missing env vars
surface as MissingEnvSecretError (from secret-resolver), which
callers typically print with the variable name for the user to fix.
Exchange client credentials for an access token.
Secret values in
credentials.client_id/client_secretmay be$ENV:VARreferences — they are resolved here at exchange time. Missing env vars surface asMissingEnvSecretError(fromsecret-resolver), which callers typically print with the variable name for the user to fix.