将hmac添加到PHP中已存在的哈希

Now, lets say that i have this hash:
Llama = ad4ba4cc53b9913beebd2b92da5ef2263e791d64

How can i add a hmac to a already generated hash?

Here is an example:

Llama = ad4ba4cc53b9913beebd2b92da5ef2263e791d64
Llama + hmac(123) = faf30b3b89da5ee9c54866d71000058da1f82148
Llama(The hash from above) + hmac(123) = 05313f6a55f5d7bf4ee42d8c66c20b37d1e2f46c

For this example im using sha1 but im going to use sha512. Write if you need some more details.

The reason why i want to do this is that i want to encrypt the users password on the client side and match it in my MySQl database. But, i do not want my hmac exposed to the public by writing it in the javascript code.

Is this even possible?

Thanks in advance!