@Test
    void verifyOperationWithValidTicketAsJwtPlain() throws Throwable {
        val request = getHttpRequestForEndpoint(OidcConstants.INTROSPECTION_URL);
        val response = new MockHttpServletResponse();
        request.addHeader(HttpHeaders.ACCEPT, OAuth20Constants.INTROSPECTION_JWT_HEADER_CONTENT_TYPE);

        val accessToken = getAccessToken(UUID.randomUUID().toString());
        val value = EncodingUtils.encodeBase64((accessToken.getClientId() + ":secret").getBytes(StandardCharsets.UTF_8));
        request.addHeader(HttpConstants.AUTHORIZATION_HEADER, HttpConstants.BASIC_HEADER_PREFIX + value);

        val oidcRegisteredService = getOidcRegisteredService(accessToken.getClientId());
        oidcRegisteredService.setIntrospectionSignedResponseAlg(null);
        servicesManager.save(oidcRegisteredService);
        ticketRegistry.addTicket(accessToken);
        request.addParameter(OAuth20Constants.TOKEN, accessToken.getId());
        val result = oidcIntrospectionEndpointController.handleRequest(request, response);
        assertInstanceOf(PlainJWT.class, JWTParser.parse(result.getBody().toString()));
        assertEquals(OAuth20Constants.INTROSPECTION_JWT_HEADER_CONTENT_TYPE, result.getHeaders().getContentType().toString());
    }
This is {@link OidcIntrospectionEndpointControllerTests}.

@author Misagh Moayyed
@since 6.1.0
support/cas-server-support-oidc/src/test/java/org/apereo/cas/oidc/web/controllers/OidcIntrospectionEndpointControllerTests.java