code: func (t *TokensClient) PostUpgradeEdDSAAuth(ctx context.Context, token, hmac string,
  	sig, publicKey *base64.Value) (*envelope.Token, error) {
  	authReq := authTokenUpgradeEdDSARequest{
  		Type:      primitive.AuthToken,
  		TokenSig:  sig,
  		PublicKey: publicKey,
  		TokenHMAC: hmac,
  	}
  
  	return t.postAuthWorker(ctx, token, &authReq)
  }
docs: // PostUpgradeEdDSAAuth requests an auth token from the registry while
  // upgrading the user from HMAC based authentication to EdDSA