Fix "BadRequest" issue with WebApps InstallSiteExtensions

[Denifia]

When adding a site extension to a web app using the following code, I receive a CloudException "Operation returned an invalid status code 'BadRequest'".

Azure
  .Configure()
  .Authenticate(credentials)
  .WithSubscription("SubscriptionId")
  .WebApps
  .Inner
  .InstallSiteExtensionAsync("ResourceGroupName", "WebAppName", "ExtensionName");

After investigation, I found that the underlying Microsoft.Azure.Management.AppService.Fluent.WebAppsOperations.BeginInstallSiteExtensionWithHttpMessagesAsync method sends no Content in its _httpRequest. Changing the auto generated code to send an empty object fixed the issue.

public async Task<AzureOperationResponse<SiteExtensionInfoInner>> BeginInstallSiteExtensionWithHttpMessagesAsync(string resourceGroupName, string name, string siteExtensionId, Dictionary<string, List<string>> customHeaders = null, CancellationToken cancellationToken = default(CancellationToken))
{
    ...

    // Serialize Request
    string _requestContent = null;

    // Added the following 3 lines
    _requestContent = Rest.Serialization.SafeJsonConvert.SerializeObject(new object(), Client.SerializationSettings);
    _httpRequest.Content = new StringContent(_requestContent, System.Text.Encoding.UTF8);
    _httpRequest.Content.Headers.ContentType = System.Net.Http.Headers.MediaTypeHeaderValue.Parse("application/json; charset=utf-8");

    ...
}

I haven't looked into why the AutoRest Code Generator is creating this code.

[vludax]

Having the same problem with this SDK: https://github.com/Azure/azure-sdk-for-net/
Should we log a separate issue there?

[hovsepm]

@vludax the issue seems to be on a server side/bad server spec here https://github.com/Azure/azure-rest-api-specs/tree/master/specification/web/resource-manager. I'd recommend opening an issue in the specs repo first.

[thecodetinker]

I've just hit this as well, still not fixed 5 years later :(