问题解决了！首先，我没有正确使用字符串函数…我最终得到了：

    let hmacResult:String = "myStringToHMAC".hmac(HMACAlgorithm.SHA1, key: "myKey")

然后我忘记了我需要对hmac结果进行base64编码。所以我将问题中链接的字符串函数修改为…

enum HMACAlgorithm {
    case MD5, SHA1, SHA224, SHA256, SHA384, SHA512

    func toCCHmacAlgorithm() -> CCHmacAlgorithm {
        var result: Int = 0
        switch self {
        case .MD5:
            result = kCCHmacAlgMD5
        case .SHA1:
            result = kCCHmacAlgSHA1
        case .SHA224:
            result = kCCHmacAlgSHA224
        case .SHA256:
            result = kCCHmacAlgSHA256
        case .SHA384:
            result = kCCHmacAlgSHA384
        case .SHA512:
            result = kCCHmacAlgSHA512
        }
        return CCHmacAlgorithm(result)
    }

    func digestLength() -> Int {
        var result: CInt = 0
        switch self {
        case .MD5:
            result = CC_MD5_DIGEST_LENGTH
        case .SHA1:
            result = CC_SHA1_DIGEST_LENGTH
        case .SHA224:
            result = CC_SHA224_DIGEST_LENGTH
        case .SHA256:
            result = CC_SHA256_DIGEST_LENGTH
        case .SHA384:
            result = CC_SHA384_DIGEST_LENGTH
        case .SHA512:
            result = CC_SHA512_DIGEST_LENGTH
        }
        return Int(result)
    }
}

extension String {
    func hmac(algorithm: HMACAlgorithm, key: String) -> String {
        let cKey = key.cStringUsingEncoding(NSUTF8StringEncoding)
        let cData = self.cStringUsingEncoding(NSUTF8StringEncoding)
        var result = [CUnsignedChar](count: Int(algorithm.digestLength()), repeatedValue: 0)
        CCHmac(algorithm.toCCHmacAlgorithm(), cKey!, strlen(cKey!), cData!, strlen(cData!), &result)
        var hmacData:NSData = NSData(bytes: result, length: (Int(algorithm.digestLength())))
        var hmacBase64 = hmacData.base64EncodedStringWithOptions(NSDataBase64EncodingOptions.Encoding76CharacterLineLength)
        return String(hmacBase64)
    }
}

这给了我正确的结果

lGCtbW+DNHFraNoxPGK3trgM/98=