Affected: Go: github.com/getkin/kin-openapi

### Summary `ValidationHandler.Load()` in `getkin/kin-openapi` silently replaces a nil `AuthenticationFunc` with `NoopAuthenticationFunc`, which always returns `nil` without performing any credential check. Because this substitution happens unconditionally when the caller omits the field, every OpenAPI `security` requirement declared in the spec is silently satisfied for unauthenticated requests. An unauthenticated remote attacker can reach handlers for routes whose OpenAPI operation requires an API key, OAuth token, or any other security scheme if the application relies on `ValidationHandler` as its enforcement middleware.

### Details `ValidationHandler` is an HTTP middleware exported by `openapi3filter` that validates incoming requests and responses against a loaded OpenAPI specification. Its `Load()` method initialises default fields before the handler begins serving:

```go // openapi3filter/validation_handler.go:47-49 if h.AuthenticationFunc == nil { h.AuthenticationFunc = NoopAuthenticationFunc } ```

`NoopAuthenticationFunc` is defined as:

```go // openapi3filter/validation_handler.go:17-18 func NoopAuthenticationFunc(context.Context, *AuthenticationInput) error { return nil } ```

It always returns `nil`, meaning every security scheme check it handles is automatically approved.

When a request arrives, `ServeHTTP` → `before` → `validateRequest` assembles a `RequestValidationInput` with the current `AuthenticationFunc` (now the no-op) injected into `Options`:…