Download of app resource failes with SSL/TLS error

[mastersign]

The WebClient fails to establish some HTTPS connections.

[mastersign]

The reason is the default setting for the allowed security protocols in System.Net.ServicePointManager.SecurityProtocol. The static property supports the flag enum type System.Net.SecurityProtocolType wich currently contains the following members: Ssl3, Tls, Tls11, Tls12.

After setting ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12 the former failing connections do work.

[mastersign]

There should be a configuration property of type list, which sets the allowed security protocols.
The property could be named HttpsSecurityProtocols and should be parsed into the flag combination of the SecurityProtocolType enum.