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:
NSAppTransportSecurity
NSExceptionDomains
yourserver.com
NSIncludesSubdomains
NSTemporaryExceptionAllowsInsecureHTTPLoads
NSTemporaryExceptionMinimumTLSVersion
TLSv1.1
But What If I Don’t Know All the Insecure Domains I Need to Use?
Use following key in your Info.plist
NSAppTransportSecurity
NSAllowsArbitraryLoads
For more detail you can get from this link.