In iOS 10+, the TLS string MUST be of the form "TLSv1.0". It can't just be "1.0". (Sigh)
The following combination of the other Answers works.
Let's say you are trying to connect to a host (YOUR_HOST.COM) that only has TLS 1.0.
Add these to your app's Info.plist
<key>NSAppTransportSecurity</key>
<dict>
<key>NSExceptionDomains</key>
<dict>
<key>YOUR_HOST.COM</key>
<dict>
<key>NSIncludesSubdomains</key>
<true/>
<key>NSTemporaryExceptionAllowsInsecureHTTPLoads</key>
<true/>
<key>NSTemporaryExceptionMinimumTLSVersion</key>
<string>TLSv1.0</string>
<key>NSTemporaryExceptionRequiresForwardSecrecy</key>
<false/>
</dict>
</dict>
</dict>