Fix: do not use (secured) theme in login page

closes #2218

Author: erikpetzold

spring-boot-admin-samples/spring-boot-admin-sample-servlet/src/main/java/de/codecentric/boot/admin/SecuritySecureConfig.java

@@ -65,7 +65,6 @@ protected SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
 
 		http.authorizeHttpRequests((authorizeRequests) -> authorizeRequests //
 				.requestMatchers(new AntPathRequestMatcher(this.adminServer.path("/assets/**"))).permitAll() // <1>
-				.requestMatchers(new AntPathRequestMatcher(this.adminServer.path("/variables.css"))).permitAll()
 				.requestMatchers(new AntPathRequestMatcher(this.adminServer.path("/actuator/info"))).permitAll()
 				.requestMatchers(new AntPathRequestMatcher(adminServer.path("/actuator/health"))).permitAll()
 				.requestMatchers(new AntPathRequestMatcher(this.adminServer.path("/login"))).permitAll()

spring-boot-admin-samples/spring-boot-admin-sample-servlet/src/main/resources/application.yml

@@ -50,6 +50,7 @@ spring:
               de-service-test-5: A large content
               de-service-test-6: A large content
             kubectl.kubernetes.io/last-applied-configuration: '{"name":"jvm.threads.peak","description":"The peak live thread count since the Java virtual machine started or peak was reset","baseUnit":"threads","measurements":[{"statistic":"VALUE","value":64.0}],"availableTags":[]}'
+          prefer-ip: true
   config:
     import: optional:configserver:http://localhost:8888/
   jmx:

spring-boot-admin-server-ui/src/main/frontend/login.css

@@ -17,8 +17,24 @@
 @tailwind components;
 @tailwind utilities;
 
+:root {
+    --bg-color-start: #71e69c;
+    --bg-color-stop: #09351a;
+}
+
+.bg-color-start {
+    transition: 0.4s ease;
+    stop-color: var(--bg-color-start);
+}
+
+.bg-color-stop {
+    transition: 0.4s ease;
+    stop-color: var(--bg-color-stop);
+}
+
+
 body {
-  font-family: BlinkMacSystemFont, -apple-system, Segoe UI, Roboto, Oxygen,
+    font-family: BlinkMacSystemFont, -apple-system, Segoe UI, Roboto, Oxygen,
     Ubuntu, Cantarell, Fira Sans, Droid Sans, Helvetica Neue, Helvetica, Arial,
     sans-serif;
 }

spring-boot-admin-server-ui/src/main/frontend/login.html

@@ -24,8 +24,6 @@
     <meta name="format-detection" content="telephone=no,email=no" />
     <meta name="theme-color" content="#42d3a5" />
 
-    <link href="/variables.css" rel="stylesheet" />
-
     <link
       rel="shortcut icon"
       th:href="${uiSettings.favicon}"