阿里云函数计算签名认证（iOS实现细节备注）

1、使用第三方库 AFNetworking进行网络请求。
2、阿里云函数计算签名认证文档
3、文档中添加 CanonicalizedFCHeaders 可以不用添加，CanonicalizedResource如何没有设置Path，在末尾加入“/”就可以了。
4、主要还是 hmac-sha256 签名认证，在实现过程中转base64的问题。
下面则是实现代码：

+ (AFHTTPSessionManager *)httpSessionManager:(NSString *)url{
    AFHTTPSessionManager *sessionManager = [[AFHTTPSessionManager alloc] initWithBaseURL:[NSURL URLWithString:url]];
    sessionManager.requestSerializer = [AFJSONRequestSerializer serializer];
    sessionManager.responseSerializer = [AFJSONResponseSerializer serializer];
    sessionManager.responseSerializer.acceptableContentTypes = [NSSet setWithObjects:@"application/json", nil];
    [sessionManager.requestSerializer setValue:[YTDWindingCalculatorHttp aliSignature:sessionManager] forHTTPHeaderField:@"Authorization"];
    return sessionManager;
}

+ (NSString *)aliSignature:(AFHTTPSessionManager *)sessionManager{
    NSString *accessKeyID = @"xxxxxx";
    NSString *accessKeySecret = @"xxxx";
    NSString *authorization = [NSString stringWithFormat:@"FC %@:",accessKeyID];
    NSMutableArray *signatureArray = [NSMutableArray array];
    [signatureArray addObject:@"POST"];
    [signatureArray addObject:@""];
    [signatureArray addObject:@"application/json"];
    NSString *date = [YTDWindingCalculatorHttp rfc1123String];
    [signatureArray addObject:date];
    [signatureArray addObject:@"/\n"];
    
    //请求头添加content-type 和 date
    [sessionManager.requestSerializer setValue:sessionManager.responseSerializer.acceptableContentTypes.allObjects.firstObject forHTTPHeaderField:@"content-type"];
    [sessionManager.requestSerializer setValue:date forHTTPHeaderField:@"date"];

    NSString *signature = [signatureArray componentsJoinedByString:@"\n"];
    signature = [YTDWindingCalculatorHttp hmac:signature withKey:accessKeySecret];
    
    authorization = [NSString stringWithFormat:@"%@%@",authorization,signature];
    return authorization;
}

+ (NSString *)hmac:(NSString *)content withKey:(NSString *)secret{
    const char *cKey  = [secret cStringUsingEncoding:NSUTF8StringEncoding];
    const char *cData = [content cStringUsingEncoding:NSUTF8StringEncoding];// 有可能有中文 所以用NSUTF8StringEncoding -> NSASCIIStringEncoding
    unsigned char cHMAC[CC_SHA256_DIGEST_LENGTH];
    CCHmac(kCCHmacAlgSHA256, cKey, strlen(cKey), cData, strlen(cData), cHMAC);
    NSData *HMACData = [NSData dataWithBytes:cHMAC length:sizeof(cHMAC)];
    NSData *base64Data = [HMACData base64EncodedDataWithOptions:NSDataBase64Encoding64CharacterLineLength];
    return [[NSString alloc] initWithData:base64Data encoding:NSUTF8StringEncoding];
}

+ (NSString *)rfc1123String{
    time_t date = (time_t)[[NSDate date] timeIntervalSince1970];
    struct tm timeinfo;
    gmtime_r(&date, &timeinfo);
    char buffer[32];
    size_t ret = strftime_l(buffer, sizeof(buffer), "%a, %d %b %Y %H:%M:%S GMT", &timeinfo, NULL);
    if (ret) {
        return @(buffer);
    } else {
        return nil;
    }
}