web-api-project | Web API Project. - | REST library

I upgraded my asp.net web app (targetFramework 4.5.2) from mvc 4 to 5 according to this link. The solution compiles without errors however at runtime I get:

The inheritance security rules were violated when the member "Autofac.Integration.Mvc.AutofacDependencyResolver.GetService (System.Type)" was overwritten. The security access of the overriding method must match the security access of the overwritten method.

I searched the forum but none of the related posts could help me to pin down the origin of the error. Trying to upgrade Autofac.Mcv4 to 5 (as suggested in the posts) failed (-> Autofac.Mcv5 does not target frameWork 4.5.2). Changing the targetFramework to 4.6 and 4.6.1 also did not allow to install Autofac.Mcv5.

Below I have listed the relevant packages installed in the main project:

I have had to take a very old project out of it's dusty box and upgrade it from 4 to 5 and I followed the guidance on the MS Site (https://docs.microsoft.com/en-us/aspnet/mvc/overview/releases/how-to-upgrade-an-aspnet-mvc-4-and-web-api-project-to-aspnet-mvc-5-and-web-api-2) and it all works perfect locally on my dev machine. Yep it works on my machine so ship it right....

Well No because I publish to the server and this is where the issues start as I keep getting errors saying:

Description: An error occurred during the processing of a configuration file required to service this request. Please review the specific error details below and modify your configuration file appropriately.

Parser Error Message: The 'targetFramework' attribute in the element of the Web.config file is used only to target version 4.0 and later of the .NET Framework (for example, ''). The 'targetFramework' attribute currently references a version that is later than the installed version of the .NET Framework. Specify a valid target version of the .NET Framework, or install the required version of the .NET Framework.

I have checked that the Web.Config file has the Target set to 4.7.1 and on the server the current version is 4.7.2 so where am I going wrong.

The line in the Web.Config that is being referenced is:

If you are using Azure Web Apps to host your web application (let it be an ASP.NET MVC web app) you do not have the possibility to set up the IIS behind the Azure Web App to accept client certificates through an HTTPS connection. My application has some Web API endpoints that would be only accessible if the user has the correct certificate with the allowed thumbprint. However, I have other endpoints as well (and of course the website) that would be accessible without a client certificate. So in my case the only way is to accept client certificates.

I am not sure about that, but if I know well I can still get the client certificate by using OWIN while the SSL Settings in IIS is set to Ignore. If I use OWIN and go through the OWIN environment I can see a key called ssl.LoadClientCertAsync.

I am implementing endpoints that a third-party service will call, so I have no control over the content of the request. I know that there is a ssl.ClientCertificate key, with type X509Certificate, but in my case this key doesn't exist.

I have found some C# solution about using this ssl.LoadClientCertAsync key to get the certificate like in the CheckClientCertificate method of Katana or the solution in this C# Corner article. In every solution that I can find in the net, the author gets this type as a Func and then calls this task, by for example using the await operator.

I'm new to c# and asp.net web api.
I'm working with Microsoft Visual Studios 2015 Community Edition.
A few days back i got an old Code. It used the old NuGet-Packages of Microsoft.AspNet.WebAPi(Client/Core/WebHost)(~v4.2).
Then i installed/updated the new Versions (~v5.2.3).
I did that in order to use the Attribute Routing of Web API v2.
I changed some stuff in order to accommodate the version changes. How to Upgrade an ASP.NET Project
I did most of the Steps described in the Link. I didn't do the Steps to change the config Files in the View Folder, because this project doesn't have a View.
The I added 1 simple Methode with Route Attribute and added Route Attribute to an existing Methode

Sample 1: