It seems you had a bad time learning ASP.NET, but in my experience what you're asking for is not difficult at all.

You have to: 1. [Optional] Define a DTO that deserializes { "foo" : { "bar" : "baz" }} to an object 2. Write a class that subclasses Controller 3. Write a method, call it whatever you want, that accepts a JObject or one of your DTO types. 4. Add the attribute [HttpPut("ping/pong/yolo")] to tell the framework this method should be bound to PUTs for that path. 5. Write your business logic.

Is that blood-crying inducing? No.

Without decent documentation, it is.

something like

app.MapPut("ping/pong/yolo", ctx => ...);

and in there you read the Body as string ... it should be a one liner?

app.MapPut("ping/pong/yolo", ([FromBody] Payload request) => {...});

record Payload(Foo Foo);

record Foo(string Bar);

or

app.MapPut("ping/pong/yolo", (JsonElement json) => {...});

Basically, just avoid outdated blog posts and articles :D

this looks like asp.net core

No one in their sane mind would use ASP.NET for new projects (it is legacy and a business risk) nowadays so it's reasonable to assume that everyone means ASP.NET Core given the .NET 7 context.

the context was asp.net mvc specifically

ASP.NET MVC is dead. It has been over 6 years; you need to update yourself.