As accepted answer has provided required info, and for more info about using and disabling App Transport Security one can find more on this.
For Per-Domain Exceptions add these to the Info.plist:
<key>NSAppTransportSecurity</key>
<dict>
<key>NSExceptionDomains</key>
<dict>
<key>yourserver.com</key>
<dict>
<!--Include to allow subdomains-->
<key>NSIncludesSubdomains</key>
<true/>
<!--Include to allow HTTP requests-->
<key>NSTemporaryExceptionAllowsInsecureHTTPLoads</key>
<true/>
<!--Include to specify minimum TLS version-->
<key>NSTemporaryExceptionMinimumTLSVersion</key>
<string>TLSv1.1</string>
</dict>
</dict>
</dict>
But What If I Don’t Know All the Insecure Domains I Need to Use?
Use following key in your Info.plist
<key>NSAppTransportSecurity</key>
<dict>
<!--Include to allow all connections (DANGER)-->
<key>NSAllowsArbitraryLoads</key>
<true/>
</dict>
For more detail you can get from this link.