Calculate hash from full (RAW) request body

I’m quite new to Postman, so sorry if I ask question that was answered before (I didn’t found anything similar).
I’m trying to implement HMAC authentication schema for my requests.
As part of hash I need to calculate I need MD5 from body.
I’ve posted same question on Stackoverflow but I was asked by @sivcan to post that question in Postman community.

When I do GET request everything works fine, but when I form-data with files I can’t calculate MD5 from body, because I don’t have access to it.
Please take a look at my github issue.

How can this be done right now inside Postman native app? Is this even possible?

As mentioned by @kamalaknn in this comment, we do not allow access to the request body with the file contents in the pre-request scripts.

Just wanted to specify here in case other people stumble upon this issue here.

@deepak.pathania so how can I solve this?
Any plans to add this as supported (build in) authentication method?

We do have plans to support custom authentication methods, this would most certainly be handled by that. Unfortunately, we do not intend to support this as a built-in authentication method for the reasons explained in the GitHub thread.

@deepak.pathania any news about custom authentication methods?
Currently, I have C# app just to test that HMAC authentication and I would like to replace that with Postman.