CredentialsFromKeychainItem.swift

static func make(withKeychainItem keychainItem: SecKeychainItem) -> Credentials? {
            var attributeTags = [SecItemAttr.accountItemAttr.rawValue]
            var formatConstants = [UInt32(CSSM_DB_ATTRIBUTE_FORMAT_STRING)]
            var attributeInfo = SecKeychainAttributeInfo(count: 1, tag: &attributeTags, format: &formatConstants)
            var attributeList: UnsafeMutablePointer<SecKeychainAttributeList>? = nil
            
            var passwordLength: UInt32 = 0
            var passwordPointer: UnsafeMutablePointer<Void>? = nil
            
            let status = SecKeychainItemCopyAttributesAndData(keychainItem,
                                                              &attributeInfo, nil, &attributeList,
                                                              &passwordLength, &passwordPointer)
            
            guard status == errSecSuccess else {
                return nil
            }
            
            let accountAttribute = attributeList?.pointee.attr.pointee
            let account = String(bytesNoCopy: (accountAttribute?.data)!, length: Int((accountAttribute?.length)!),
                                 encoding: String.Encoding.utf8, freeWhenDone: false)!
            
            let password = String(bytesNoCopy: passwordPointer!, length: Int(passwordLength),
                                  encoding: String.Encoding.utf8, freeWhenDone: false)!
            
            SecKeychainItemFreeAttributesAndData(attributeList, passwordPointer)
            
            return Credentials(email: account, password: password)
        }