转到Gmail API服务帐户

I would like to send email via Gmail using a service account API. I am able to do this with a Client ID and Client Secret, but a service account doesn't have a client secret. Here's what I do have:

{
  "type": "service_account",
  "project_id": "my-project-id",
  "private_key_id": "107...",
  "private_key": "-----BEGIN PRIVATE KEY-----
MII...=
-----END PRIVATE KEY-----
",
  "client_email": "something@something.iam.gserviceaccount.com",
  "client_id": "103...",
  "auth_uri": "https://accounts.google.com/o/oauth2/auth",
  "token_uri": "https://accounts.google.com/o/oauth2/token",
  "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
  "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/something%40something.iam.gserviceaccount.com"
}

How can I use this information to connect and send an email? All the documentation seems to reference non-service accounts.