服務端配置

nginx關鍵配置如下：

listen       443;
server_name  localhost;
ssl on;
ssl_certificate      /usr/local/opt/nginx/certificates/server.cer;
ssl_certificate_key  /usr/local/opt/nginx/certificates/server.key.pem;
ssl_client_certificate /usr/local/opt/nginx/certificates/ca.cer;
ssl_verify_client    on;

ssl開啟https

ssl_certificate是服務端證書的路徑，ssl_certificate_key是服務端私鑰的路徑

ssl_verify_client是配置雙向認證（client certificate）

ssl_client_certificate是簽發客戶端證書的根證書

為什麼是根證書，因為可以簽發很多客戶端證書，只要是由該根證書簽發的，服務端都視為認證通過

配置完成以後，一般需要把80端口的http請求跳轉到443端口，否則用戶可以通過80端口以http方式訪問，就失去了安全保護的意義

客戶端代碼

在網上找了很多ios client certificate的帖子，要麼是代碼不全，要麼是很老的帖子，還是用的NSURLConnection，delegate method都deprecated了，最後找了一個代碼片段，改了一下

NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
    
NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil];
    
NSURL *url = [NSURL URLWithString:@"https://localhost/svc/portal/setting"];
    
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:url];
[request setCachePolicy:NSURLRequestReloadIgnoringLocalCacheData];
[request setHTTPShouldHandleCookies:NO];
[request setTimeoutInterval:30];
[request setHTTPMethod:@"GET"];
    
NSURLSessionDataTask *task = [session dataTaskWithURL:url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
    NSString *message = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    NSLog(@"%@", message);
}];
    
[task resume];

上面的代碼片段，是用NSURLSessionDataTask發起https請求。在ssl握手階段，會調用2次下面的delegate method

- (void)URLSession:(NSURLSession *)session didReceiveChallenge:(NSURLAuthenticationChallenge *)challenge completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition disposition, NSURLCredential *credential))completionHandler
{
    NSString *method = challenge.protectionSpace.authenticationMethod;
    NSLog(@"%@", method);
    
    if([method isEqualToString:NSURLAuthenticationMethodServerTrust]){
        
        NSString *host = challenge.protectionSpace.host;
        NSLog(@"%@", host);
        
        NSURLCredential *credential = [NSURLCredential credentialForTrust:challenge.protectionSpace.serverTrust];
        completionHandler(NSURLSessionAuthChallengeUseCredential, credential);
        return;
    }

    NSString *thePath = [[NSBundle mainBundle] pathForResource:@"client" ofType:@"p12"];
    NSData *PKCS12Data = [[NSData alloc] initWithContentsOfFile:thePath];
    CFDataRef inPKCS12Data = (CFDataRef)CFBridgingRetain(PKCS12Data);
    SecIdentityRef identity;
    
    // 讀取p12證書中的內容
    OSStatus result = [self extractP12Data:inPKCS12Data toIdentity:&identity];
    if(result != errSecSuccess){
        completionHandler(NSURLSessionAuthChallengeCancelAuthenticationChallenge, nil);
        return;
    }
    
    SecCertificateRef certificate = NULL;
    SecIdentityCopyCertificate (identity, &certificate);
    
    const void *certs[] = {certificate};
    CFArrayRef certArray = CFArrayCreate(kCFAllocatorDefault, certs, 1, NULL);
    
    NSURLCredential *credential = [NSURLCredential credentialWithIdentity:identity certificates:(NSArray*)CFBridgingRelease(certArray) persistence:NSURLCredentialPersistencePermanent];
    
    completionHandler(NSURLSessionAuthChallengeUseCredential, credential);
}

-(OSStatus) extractP12Data:(CFDataRef)inP12Data toIdentity:(SecIdentityRef*)identity {
    
    OSStatus securityError = errSecSuccess;
    
    CFStringRef password = CFSTR("the_password");
    const void *keys[] = { kSecImportExportPassphrase };
    const void *values[] = { password };
    
    CFDictionaryRef options = CFDictionaryCreate(NULL, keys, values, 1, NULL, NULL);
    
    CFArrayRef items = CFArrayCreate(NULL, 0, 0, NULL);
    securityError = SecPKCS12Import(inP12Data, options, &items);
    
    if (securityError == 0) {
        CFDictionaryRef ident = CFArrayGetValueAtIndex(items,0);
        const void *tempIdentity = NULL;
        tempIdentity = CFDictionaryGetValue(ident, kSecImportItemIdentity);
        *identity = (SecIdentityRef)tempIdentity;
    }
    
    if (options) {
        CFRelease(options);
    }
    
    return securityError;
}

上面的代碼片段，即拷即用，希望能有所幫助。這個方法會被調用2次，第一次是ios app驗證server的階段，第二次是server驗證ios app的階段，即client certificate。關鍵是每個階段的校驗完成以後，要調用completionHandler方法。網上的大部分帖子都是

[[challenge sender] useCredential:credential forAuthenticationChallenge:challenge];

這行代碼是無效的