使用服务器信任证书，访问https服务器
参考ASIHHPRequest开源项目中的ClientCertificateTests.m源码。
链接：https://github.com/pokeb/asi-http-request/blob/master/Classes/Tests/ClientCertificateTests.m
以及：http://developer.apple.com/library/mac/#documentation/Security/Conceptual/CertKeyTrustProgGuide/iPhone_Tasks/iPhone_Tasks.html
+ (void)testClientCertificate {NSURL *httpsUrl = [NSURL URLWithString:@"https://xxxxxx.xx.xx"];ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:httpsUrl];SecIdentityRef identity = NULL;SecTrustRef trust = NULL; //绑定证书，证书放在Resources文件夹中NSData *PKCS12Data = [NSData dataWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"client" ofType:@"p12"]];[HttpsTestViewController extractIdentity:&identity andTrust:&trust fromPKCS12Data:PKCS12Data];request = [ASIHTTPRequest requestWithURL:httpsUrl];[request setClientCertificateIdentity:identity];[request setValidatesSecureCertificate:NO];[request startSynchronous];error = [request error];if (!error) {NSString *response = [request responseString];NSLog(@"response is : %@",response);} else {NSLog(@"Failed to save to data store: %@", [error localizedDescription]);NSLog(@"%@",[error userInfo]);}}+ (BOOL)extractIdentity:(SecIdentityRef *)outIdentity andTrust:(SecTrustRef*)outTrust fromPKCS12Data:(NSData *)inPKCS12Data {OSStatus securityError = errSecSuccess;CFStringRef password = CFSTR("xxxxxx"); //证书密码const void *keys[] = { kSecImportExportPassphrase }; const void *values[] = { password };CFDictionaryRef optionsDictionary = CFDictionaryCreate(NULL, keys,values, 1,NULL, NULL); CFArrayRef items = CFArrayCreate(NULL, 0, 0, NULL);//securityError = SecPKCS12Import((CFDataRef)inPKCS12Data,(CFDictionaryRef)optionsDictionary,&items);securityError = SecPKCS12Import((CFDataRef)inPKCS12Data,optionsDictionary,&items); if (securityError == 0) { CFDictionaryRef myIdentityAndTrust = CFArrayGetValueAtIndex (items, 0);const void *tempIdentity = NULL;tempIdentity = CFDictionaryGetValue (myIdentityAndTrust, kSecImportItemIdentity);*outIdentity = (SecIdentityRef)tempIdentity;const void *tempTrust = NULL;tempTrust = CFDictionaryGetValue (myIdentityAndTrust, kSecImportItemTrust);*outTrust = (SecTrustRef)tempTrust;} else {NSLog(@"Failed with error code %d",(int)securityError);return NO;}return YES;}