HMAC algorithm for iOS

hmac.swift

import Foundation

//You have to create a bridging header in your project containing:
// #import <CommonCrypto/CommonHMAC.h>

extension String {
    
    func digestHMac256(key: String) -> String! {
        
        let str = self.cStringUsingEncoding(NSUTF8StringEncoding)
        let strLen = self.lengthOfBytesUsingEncoding(NSUTF8StringEncoding)

        let digestLen = Int(CC_SHA256_DIGEST_LENGTH)
        let result = UnsafeMutablePointer<CUnsignedChar>.alloc(digestLen)
        
        let keyStr = key.cStringUsingEncoding(NSUTF8StringEncoding)
        let keyLen = key.lengthOfBytesUsingEncoding(NSUTF8StringEncoding)

        let algorithm = CCHmacAlgorithm(kCCHmacAlgSHA256)
        
        CCHmac(algorithm, keyStr!, keyLen, str!, strLen, result)
        
        let data = NSData(bytesNoCopy: result, length: digestLen)
            
        let hash = data.base64EncodedStringWithOptions(.allZeros)
    
        return hash
    }
}

Based on: http://stackoverflow.com/questions/24099520/commonhmac-in-swift

and http://www.jokecamp.com/blog/examples-of-creating-base64-hashes-using-hmac-sha256-in-different-languages/