As @schroeder pointed out in the comments, this site assesses the client capabilities and reports on them in the response:
- The site doesn't allow a POST; it requires a GET. Our app could be configured either way, but some might not.
- The site won't require TLS 1.2 in a way which emulates the behavior of sites which do.
As @paj28 pointed out in the comments, this site will only work if TLS 1.2 is available:
Unfortunately, our app did not work seamlessly on Windows 2008 R2. Trying the FancySSL site, it got this error:
The handle is in the wrong state for the requested operation
Trying the SSLLabs site, it got these results:
- TLS 1.2: No
- TLS 1.1: No
- TLS 1.0: Yes*
- SSL 3: Yes*
- SSL 2: No
When we run the same app on a Windows 10 or Windows Server 2012 R2, the app doesn't encounter the error and SSLLabs reports TLS 1.2 as available.
Another option I discovered: