That worked!
On the front end I changed my auth0.webAuth to
auth0 = new auth0.WebAuth({
clientID: env.authClientId,
domain: env.authDomain,
responseType: 'token id_token',
redirectUri: env.authCallbackUrl,
scope: 'openid',
audience: env.authAudience
});
Then in the Http headers to the backend i use:
'Authorization': `Bearer ${this.accessToken}`