fix(observability-proxy): accept the bearer scheme in any case

The authorization scheme is case-insensitive, and kube-apiserver
accepts "bearer" as well as "Bearer", so a client that works against
the API server got 401 from the proxy with the same header.

Assisted-by: LLM
Signed-off-by: ZverGuy <maximbel2003@gmail.com>

internal/observabilityproxy/server.go

@@ -300,8 +300,8 @@ func (s *Server) readForm(w http.ResponseWriter, r *http.Request) *HTTPError {
 }
 
 func (s *Server) authorize(r *http.Request, route Route) (string, *HTTPError) {
-	token, ok := strings.CutPrefix(r.Header.Get("Authorization"), "Bearer ")
-	if !ok {
+	scheme, token, _ := strings.Cut(r.Header.Get("Authorization"), " ")
+	if !strings.EqualFold(scheme, "Bearer") {
 		return "", errorf(http.StatusUnauthorized, "missing bearer token")
 	}
 	user, err := s.auth.Authenticate(r.Context(), strings.TrimSpace(token))

internal/observabilityproxy/server_test.go

@@ -452,3 +452,21 @@ func TestServerTailLongLine(t *testing.T) {
 		t.Fatalf("long line not streamed intact: got %d bytes", len(body))
 	}
 }
+
+// The auth scheme is case-insensitive (RFC 9110, section 11.1), as
+// kube-apiserver reads it.
+func TestServerBearerSchemeCase(t *testing.T) {
+	h := newHarness(t, Config{}, nil)
+	for _, auth := range []string{"Bearer good", "bearer good", "BEARER good"} {
+		resp := h.do(http.MethodGet, logsRoot+"query", "", nil, map[string]string{"Authorization": auth})
+		_ = resp.Body.Close()
+		if resp.StatusCode != http.StatusOK {
+			t.Errorf("Authorization %q answered %d, want 200", auth, resp.StatusCode)
+		}
+	}
+	resp := h.do(http.MethodGet, logsRoot+"query", "", nil, map[string]string{"Authorization": "Basic good"})
+	_ = resp.Body.Close()
+	if resp.StatusCode != http.StatusUnauthorized {
+		t.Errorf("Basic scheme answered %d, want 401", resp.StatusCode)
+	}
+}