[management,proxy] Use single-use codes for OIDC session handoff (#7635)

* Generalize PKCE verifier store into SingleUseStore

* Generalize PKCE verifier store into SingleUseStore

* Extend single-use store to generate one-time retrieval codes

* Hand off proxy OIDC session via one-time code instead of URL token

* Use the single-use store in integration tests

* Read active proxy versions by cluster

* Detect proxy clusters that support session codes

* Bind OIDC session handoff mode to signed state

* Deprecate legacy OIDC session token handoff

* Remove unrelated session code test stub

* fix tests

* fix merge

* Fix session code compatibility detection

* Isolate proxy session codes in shared cache

* bump min session version

proxy/internal/auth/middleware_test.go

@@ -783,6 +783,12 @@ func TestWasCredentialSubmitted(t *testing.T) {
 			query:    url.Values{"session_token": {"abc123"}},
 			expected: true,
 		},
+		{
+			name:     "OIDC code in query",
+			method:   auth.MethodOIDC,
+			query:    url.Values{"session_code": {"abc123"}},
+			expected: true,
+		},
 		{
 			name:     "OIDC token not in query",
 			method:   auth.MethodOIDC,
@@ -1571,3 +1577,23 @@ func TestProtect_TunnelPeerFastPath_TakesPathWithInboundMarker(t *testing.T) {
 	assert.Equal(t, http.StatusOK, rec.Code,
 		"a successful tunnel-peer validation must forward to the next handler")
 }
+
+func TestStripSessionTokenParam(t *testing.T) {
+	cases := []struct {
+		name string
+		in   string
+		want string
+	}{
+		{"strips session_token", "https://ex.com/p?a=1&session_token=tok", "/p?a=1"},
+		{"strips session_code", "https://ex.com/p?a=1&session_code=code", "/p?a=1"},
+		{"strips both", "https://ex.com/p?session_token=tok&session_code=code&a=1", "/p?a=1"},
+		{"no-op when absent", "https://ex.com/p?a=1", "/p?a=1"},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			u, err := url.Parse(tc.in)
+			require.NoError(t, err)
+			assert.Equal(t, tc.want, stripSessionTokenParam(u))
+		})
+	}
+}