REST API flow with Xamarin async

GetPublicKeyTasks.cs

public class GetPublicKeyTasks : IRestApiCallTasks<string, Stream, PublicKeyX509Certificate>
{
		public async Task<string> BuildRequestUrlForRequestAsync( string instanceUrl )
		{
			return await Task.Factory.StartNew ( () => instanceUrl + "/-/item/v1/-/actions/getpublickey" );
		}

		public async Task<Stream> SendRequestForUrlAsync( string requestUrl )
		{
			return await this.httpClient.GetStreamAsync(requestUrl);
		}


		// disposes httpData
		public async Task<PublicKeyX509Certificate> ParseResponseDataAsync(Stream httpData)
		{
			using (Stream publicKeyStream = httpData)
			{
				Func<PublicKeyX509Certificate> syncParsePublicKey = () =>
				{
					return new PublicKeyXmlParser().Parse(publicKeyStream);
				};
				PublicKeyX509Certificate result =  await Task.Factory.StartNew(syncParsePublicKey);
				return result;
			}
		}
}

IRestApiCallTasks.cs

	public interface IRestApiCallTasks<TRequest, THttpResult, TResult>
	{
		Task<string> BuildRequestUrlForRequestAsync( TRequest request );
		Task<THttpResult> SendRequestForUrlAsync( string requestUrl );
		Task<TResult> ParseResponseDataAsync(THttpResult httpData);
	}

RestApiCallFlow.cs

	public class RestApiCallFlow
	{
		public static async Task<TResult> LoadRequestFromNetworkFlow<TRequest, THttpResult, TResult>(TRequest request, IRestApiCallTasks<TRequest, THttpResult, TResult> stages)
		{
			string requestUrl          = await stages.BuildRequestUrlForRequestAsync (request       );
			THttpResult serverResponse = await stages.SendRequestForUrlAsync         (requestUrl    );
			TResult parsedData         = await stages.ParseResponseDataAsync         (serverResponse);

			return parsedData;
		}

	}

Usage.cs

        public async Task<PublicKeyX509Certificate> GetPublicKey()
        {
			GetPublicKeyTasks taskFlow = new GetPublicKeyTasks (this.httpClient);


			PublicKeyX509Certificate result = await RestApiCallFlow.LoadRequestFromNetworkFlow(this.sessionConfig.InstanceUrl, taskFlow);
			this.publicCertifiacte = result;

			return result;
		}