getSession() doesn't work on server side when request is POST

[clueleaf]

What is the improvement or update you wish to see?

Since I faced a situation where getSession() doesn't work properly on the server side, I think this part of doc should be fixed.

next-auth/docs/docs/getting-started/client.md

Line 287 in d69f311

On the server side, **this is still available to use**, however, we recommend using `getServerSession` going forward. The idea behind this is to avoid an additional unnecessary `fetch` call on the server side. For more information, please check out [this issue](https://github.com/nextauthjs/next-auth/issues/1535).

Is there any context that might help us understand?

When using getSession() on the server side with POST request, it returns null as described here.
#7167

Does the docs page already exist? Please link to it.

next-auth/docs/docs/getting-started/client.md

Line 287 in d69f311

On the server side, **this is still available to use**, however, we recommend using `getServerSession` going forward. The idea behind this is to avoid an additional unnecessary `fetch` call on the server side. For more information, please check out [this issue](https://github.com/nextauthjs/next-auth/issues/1535).

[naokato]

If possible, I would like to continue using useSession on the server side.
I have already used it in many places, and for now, the overhead of making fetch requests each time is not a big concern for me.

[balazsorban44]

We will deprecate/stop recommending getSession server-side, as it is inefficient and can cause issues/misunderstandings. You should always use getServerSession instead.

[clueleaf]

@balazsorban44
I understand we should use getServerSession on the server side, but this issue is about documentation.
Because getSession doesn't work at all in some cases, I think the document should not be On the server side, **this is still available to use**.