Add BindJSONBody to bind the request body value kin-openapi validated

README.md

@@ -221,3 +221,26 @@ correct, media-type-defined behavior.
   their original precision, but the round-trip through JSON means struct
   field tags are honored (not raw Go field names).
 
+
+## Request body binding
+
+`BindJSONBody` is what strict net/http servers generated by `oapi-codegen` call
+to decode a JSON request body. When the request has passed through a validation
+middleware built on kin-openapi's `openapi3filter` with
+`Options.KeepValidatedValue` set (for example
+`nethttp-middleware.OapiRequestValidatorWithOptions`), the body carries the
+value the validator decoded and validated, and `BindJSONBody` binds that value
+into the request struct with `BindJSONValue` instead of decoding the body a
+second time.
+
+Binding follows `encoding/json`'s rules (struct tags, embedded structs,
+`json.Unmarshaler` / `encoding.TextUnmarshaler`, base64 for `[]byte`, `float64`
+for `any`), with one deliberate difference: object member names are matched to
+struct fields **exactly**, whereas `encoding/json` matches them
+case-insensitively. This closes the gap where `{"role":"user","ROLE":"admin"}`
+validates as `role: user` but a second `encoding/json` decode binds
+`Role: "admin"`.
+
+Without a validated value, or when the value cannot be bound into the
+destination type, `BindJSONBody` decodes the body with `encoding/json` exactly
+as before, so error responses are unchanged.