API token is invalid_token when decoding with guardian

Are you using this Auth0 Ueberauth strategy?
https://github.com/achedeuzot/ueberauth_auth0

If so, take a look at the callback functions in auth_controller.ex from the ueberauth example repo:

  def callback(%{assigns: %{ueberauth_failure: _fails}} = conn, _params) do
    conn
    |> put_flash(:error, "Failed to authenticate.")
    |> redirect(to: "/")
  end


  def callback(%{assigns: %{ueberauth_auth: auth}} = conn, _params) do
    case UserFromAuth.find_or_create(auth) do
      {:ok, user} ->
        conn
        |> put_flash(:info, "Successfully authenticated.")
        |> put_session(:current_user, user)
        |> configure_session(renew: true)
        |> redirect(to: "/")


      {:error, reason} ->
        conn
        |> put_flash(:error, reason)
        |> redirect(to: "/")
    end
  end