Hi Matt,

We've taken this up via our ticketing service, but I still wanted to write a response to your question here in case other people have the same question.

My understanding from https://developers.google.com/identity/protocols/oauth2/service-account#jwt-auth is that you can use the DEX method https://documentation.aimms.com/dataexchange/api.html#managing-jwt-tokens.

The first argument for the dex::jwt::Encode() would be the payload (which is a JSON with the claims as required by the API you're trying to use).
The second argument is the private RSA key used to sign the JWT token. This should be a private key (in JSON-format), found in your Google service account.
The third argument is an output string argument that you will use in the follow-up request in which the signed JWT token is being stored.

If that Encode procedure was handled successfully, you can use the output string argument in your 'real' request to the API. An example can be found here: https://developers.google.com/identity/protocols/oauth2/service-account#httprest (look for 'Making the access token request').

I hope this gives an idea of the steps to follow.