fix: handle preparsed body payloads in verifyAndReceive accordingly

[Uzlopak]

fixes #961

probot/probot#1955 (comment)

[github-actions]

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[AaronDewes]

This could cause problems if GitHub ever changes payload serialization, so the signature would not match...

We should check if it's possible to disable this parsing in Vercel.

[Uzlopak]

It is possible probot/probot#1955 (comment)

[G-Rath]

Seems like you don't even need to do that: https://vercel.com/guides/how-do-i-get-the-raw-body-of-a-serverless-function

[AaronDewes]

#963 should be a better implementation based on that guide

[Uzlopak]

I have no preference. But you should add a test to your PR.

[wolfy1339]

@Uzlopak from the discussion in #963, I think we might need to add the typeof condition here: https://github.com/probot/probot/blob/1eb03896e9772312c84f0be3da7bf3c0910797b6/src/context.ts#L72

I'm sorry if I'm wrong, but looking at the source code, my mind tells me that it is the place from where the request body is passed to this SDK.

That is the Context class, it doesn't call the webhooks at all. It only augments it.

The webhooks aren't really called anywhere, we just pass through the data from the integrated web server and do the handliin this library:
https://github.com/probot/probot/blob/1eb03896e9772312c84f0be3da7bf3c0910797b6/src/create-node-middleware.ts#L14

[wolfy1339]

Closing as per discussion in #963