Apex version to generate a multipass token for Desk.com.

Multipass.cls

public class Multipass
{
    private static String SITE_KEY =   'site_key';
    private static String API_KEY =    'api_key';
    
    public static void generate()
    {
        System.debug('== Generating ==');

        System.debug('    Create the encryption key using a 16 byte SHA1 digest of your api key and subdomain');
        Blob key = Crypto.generateDigest('SHA1', Blob.valueOf(API_KEY + SITE_KEY));

        System.debug('    Cut to correct length');
        key = EncodingUtil.base64Decode(EncodingUtil.base64Encode(key).left(22));

        System.debug('    Build json data');
        String data = JSON.serialize(new Map<String, String>{
            'uid' => '1',
            'expires' => DateTime.now().addSeconds(300).formatGMT('yyyy-MM-dd\'T\'HH:mm:ss.SSS\'Z\''),
            'customer_email' => 'john@example.com',
            'customer_name' => 'John'
        });
        System.debug('    Data: ' + data);

        System.debug('    Encrypt data using AES128-cbc');
        Blob multipass = Crypto.encryptWithManagedIV('AES128', key, Blob.valueOf(data));

        System.debug('    Base64 encode the encrypted data');
        String multipass_string = EncodingUtil.base64Encode(multipass);

        System.debug('    Build an HMAC-SHA1 signature using the encoded string and your api key');
        Blob signature = Crypto.generateMac('hmacSHA1', Blob.valueOf(multipass_string), Blob.valueOf(API_KEY));
        String signature_string = EncodingUtil.base64Encode(signature);

        System.debug('    Finally, URL encode the multipass and signature');
        multipass_string = EncodingUtil.urlEncode(multipass_string, 'UTF-8');
        signature_string = EncodingUtil.urlEncode(signature_string, 'UTF-8');

        System.debug('== Finished ==');
        System.debug('https://' + SITE_KEY + '.desk.com/customer/authentication/multipass/callback?multipass=' + multipass_string + '&signature=' + signature_string);
    }
}

@imranqurehi you'll have to generate the KEY_BASE64 string in a different environment. A ruby example is commented out in the code on the lines 9-11 but you can use PHP, .net or any other programming language that allows you to generate a SHA1 digest and cut out the first 16 bytes of that digest.

Got it working in apex . Made some changes to the code to fetch out the first 16 bytes .

blob blobToGenerateSHA = blob.valueof(API_KEY + SITE_KEY);
           system.debug('*****'+string.valueof(Crypto.generateDigest('SHA1', blobToGenerateSHA)));
           blob codeSHA = Crypto.generateDigest('SHA1', blobToGenerateSHA);
           string  b64= EncodingUtil.base64Encode(codeSHA);
           KEY_BASE64 = b64.left(22);
           System.debug('String b64: [' + KEY_BASE64 );   
           System.debug('== Generating ==');

           Blob key = EncodingUtil.base64Decode(KEY_BASE64);