verify_state_input

  def verify_state_input(fields) do
    required_fields = [:client_id, :provider, :redirect_uri, :sub]

    # Determine which keys are missing from the state input and add it to our
    # errors so that we can return exactly what we're missing to the client
    field_errors =
      required_fields
      |> Enum.reduce(%{}, fn required_key, acc ->
        has_key? =
          Enum.any?(fields, fn {input_key, _v} ->
            required_key == input_key
          end)

        if has_key?, do: acc, else: Map.put(acc, required_key, "Required field.")
      end)

    {:error,
     %MalformedInputError{
       fields: field_errors,
       message:
         "Invalid state parameters.  You must provide `client_id`, `provider`, `redirect_uri` and `sub`"
     }}
  end