Determine whether `LineAuthenticationHandler.ExchangeCodeAsync()` is necessary

[kevinchalet]

AFAICT, LineAuthenticationHandler.ExchangeCodeAsync() doesn't seem to do anything special so it's probably not necessary.

AspNet.Security.OAuth.Providers/src/AspNet.Security.OAuth.Line/LineAuthenticationHandler.cs

Lines 35 to 66 in cbbc7a1

	protected override async Task<OAuthTokenResponse> ExchangeCodeAsync([NotNull] OAuthCodeExchangeContext context)
	{
	var tokenRequestParameters = new Dictionary<string, string>
	{
	["grant_type"] = "authorization_code",
	["code"] = context.Code,
	["redirect_uri"] = context.RedirectUri,
	["client_id"] = Options.ClientId,
	["client_secret"] = Options.ClientSecret,
	};
	// PKCE https://tools.ietf.org/html/rfc7636#section-4.5, see BuildChallengeUrl
	if (context.Properties.Items.TryGetValue(OAuthConstants.CodeVerifierKey, out var codeVerifier))
	{
	tokenRequestParameters.Add(OAuthConstants.CodeVerifierKey, codeVerifier!);
	context.Properties.Items.Remove(OAuthConstants.CodeVerifierKey);
	}
	using var request = new HttpRequestMessage(HttpMethod.Post, Options.TokenEndpoint);
	request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
	request.Content = new FormUrlEncodedContent(tokenRequestParameters);
	using var response = await Backchannel.SendAsync(request, Context.RequestAborted);
	if (!response.IsSuccessStatusCode)
	{
	await Log.ExchangeCodeErrorAsync(Logger, response, Context.RequestAborted);
	return OAuthTokenResponse.Failed(new Exception("An error occurred while retrieving an access token."));
	}
	var payload = JsonDocument.Parse(await response.Content.ReadAsStringAsync(Context.RequestAborted));
	return OAuthTokenResponse.Success(payload);
	}

[martincostello]

Reviewing the code, the only difference appears to be that the OAuthHandler implementation sets HttpRequestMessage.Version.