配置https证书

后台同事给的事.pem和.key文件，项目中要用cer证书，所以要转一下

pem证书转cer证书 命令：

1.openssl pkcs12 -export -out cacert.p12 -in cacert.pem -inkey cacert.key   先转p12

2.openssl pkcs12 -in cacert.p12 -out mycerts.crt -nokeys -clcerts　　　　再转crt

3.openssl x509 -inform pem -in mycerts.crt -outform der -out mycerts.cer  最后转cer

引用证书代码：

   _sessionManager = [[AFHTTPSessionManager manager] initWithBaseURL:[NSURL URLWithString:ServerPath]];
    // 设置请求的超时时间
    _sessionManager.requestSerializer.timeoutInterval = 30.f;
    NSString *cerPath = [[NSBundle mainBundle] pathForResource:@"teststudent" ofType:@"cer"];//证书的路径   
 NSData *cerData = [NSData dataWithContentsOfFile:cerPath];
    // 使用证书验证模式
    AFSecurityPolicy *securityPolicy = [AFSecurityPolicy policyWithPinningMode:AFSSLPinningModeCertificate];
    // 如果需要验证自建证书(无效证书)，需要设置为YES
    securityPolicy.allowInvalidCertificates = YES;
    // 是否需要验证域名，默认为YES;
    securityPolicy.validatesDomainName = validatesDomainName;
    securityPolicy.pinnedCertificates = [[NSSet alloc] initWithObjects:cerData, nil];
    [_sessionManager setSecurityPolicy:securityPolicy];

AFHTTPSessionManager注意一定要 initWithBaseURL 添加baseurl，直接[AFHTTPSessionManager manager]会报错：

A security policy configured with `AFSSLPinningModeCertificate` can only be applied on a manager with a secure base URL (i.e. https)。闪退