Authenticated firebase functions with custom OpenId Connect provider

Question

I have implemented a custom oidc authentication provider with firebase. (Which was very easy!)

For reference, the oidc provider I implemented is for Xero (accounting app)

I want to implement authenticated httpsCallable functions that use the accessToken that is returned from the callback but I can't seem to access it in the firebase function.

Ultimately the getTokenSetFromDatabase function from this example is what I need to recreate somehow in firebase function: https://github.com/XeroAPI/xero-node#accounting-api

The context.auth info in the firebase functions contains some authentication data but not any jwts or tokens.

export const getTenants = functions.https.onCall(async (data, context) => {
  await xero.initialize()

  // Can I get the token set somehow from the context
  // Or do I need to save a users token in the firebase database when they login from the front end?
  const tokenSet = getTokenSetFromDatabase(context.auth?.uid)

  await xero.setTokenSet(tokenSet)

  if (tokenSet.expired()) {
    const validTokenSet = await xero.refreshToken()
    // save the new tokenset
  }

  await xero.updateTenants()

  const activeTenantId = xero.tenants[0].tenantId

  return activeTenantId
})

The console log of context.auth.token is:

{
  "name": "Jialx",
  "iss": "https://securetoken.google.com/firebase-app-name",
  "aud": "firebase-app-name",
  "auth_time": 1658994364,
  "user_id": "0000000000000000000000",
  "sub": "0000000000000000000000",
  "iat": 1659007170,
  "exp": 1659010770,
  "email": "[email protected]",
  "email_verified": false,
  "firebase": {
    "identities": { "oidc.xero": [], "email": [] },
    "sign_in_provider": "oidc.xero",
    "sign_in_attributes": {
      "at_hash": "xx-xxxx-xxxx",
      "preferred_username": "[email protected]",
      "sid": "000000000000000000000000000",
      "global_session_id": "000000000000000000000000000",
      "xero_userid": "000000000000000000000000000"
    }
  },
  "uid": "0000000000000000000000"
}