Spring Security, Webjars, and MIME type error

| java | programming | ci |

I volunteered to be JLO (Java Language Owner) at CircleCI and I am currently working on getting a sample Spring Framework project running on CircleCI 2.0. I made a simple app bootstrapped with the Spring Initializer. I included Spring Security for the first time and I decided to try out WebJars for static Javascript libraries such as bootstrap. I am using Thymeleaf for templating.The app does not actually do anything yet but I ran into a pretty strange issue today that I wanted to write up here. My home page is pretty straightforward.

<!DOCTYPE html>
<html xmlns:th="https://www.thymeleaf.org">
<head>
    <title>CircleCI Spring Demo</title>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />

<span class="p">&lt;</span><span class="nt">link</span> <span class="na">rel</span><span class="o">=</span><span class="s">"stylesheet"</span> <span class="na">th:href</span><span class="o">=</span><span class="s">"@{/webjars/bootstrap/3.3.7/css/bootstrap.min.css}"</span> <span class="p">/&gt;</span>

<span class="p">&lt;</span><span class="nt">link</span> <span class="na">rel</span><span class="o">=</span><span class="s">"stylesheet"</span> <span class="na">th:href</span><span class="o">=</span><span class="s">"@{/css/style.css}"</span> <span class="na">href</span><span class="o">=</span><span class="s">"../static/css/style.css"</span> <span class="p">/&gt;</span>



</head>
<body>


<span class="p">&lt;</span><span class="nt">nav</span> <span class="na">class</span><span class="o">=</span><span class="s">"navbar"</span><span class="p">&gt;</span>
    <span class="p">&lt;</span><span class="nt">div</span> <span class="na">class</span><span class="o">=</span><span class="s">"container"</span><span class="p">&gt;</span>
        <span class="p">&lt;</span><span class="nt">div</span> <span class="na">class</span><span class="o">=</span><span class="s">"navbar-header"</span><span class="p">&gt;</span>
            <span class="p">&lt;</span><span class="nt">a</span> <span class="na">class</span><span class="o">=</span><span class="s">"navbar-brand"</span> <span class="na">href</span><span class="o">=</span><span class="s">"#"</span><span class="p">&gt;</span>CircleCI Demo Spring<span class="p">&lt;/</span><span class="nt">a</span><span class="p">&gt;</span>
        <span class="p">&lt;/</span><span class="nt">div</span><span class="p">&gt;</span>
        <span class="p">&lt;</span><span class="nt">div</span> <span class="na">id</span><span class="o">=</span><span class="s">"navbar"</span> <span class="na">class</span><span class="o">=</span><span class="s">"collapse navbar-collapse"</span><span class="p">&gt;</span>
            <span class="p">&lt;</span><span class="nt">ul</span> <span class="na">class</span><span class="o">=</span><span class="s">"nav navbar-nav"</span><span class="p">&gt;</span>
                <span class="p">&lt;</span><span class="nt">li</span> <span class="na">class</span><span class="o">=</span><span class="s">"active"</span><span class="p">&gt;&lt;</span><span class="nt">a</span> <span class="na">href</span><span class="o">=</span><span class="s">"#"</span><span class="p">&gt;</span>Home<span class="p">&lt;/</span><span class="nt">a</span><span class="p">&gt;&lt;/</span><span class="nt">li</span><span class="p">&gt;</span>
                <span class="p">&lt;</span><span class="nt">li</span><span class="p">&gt;&lt;</span><span class="nt">a</span> <span class="na">href</span><span class="o">=</span><span class="s">"#"</span><span class="p">&gt;</span>About<span class="p">&lt;/</span><span class="nt">a</span><span class="p">&gt;&lt;/</span><span class="nt">li</span><span class="p">&gt;</span>
            <span class="p">&lt;/</span><span class="nt">ul</span><span class="p">&gt;</span>
        <span class="p">&lt;/</span><span class="nt">div</span><span class="p">&gt;</span>
    <span class="p">&lt;/</span><span class="nt">div</span><span class="p">&gt;</span>
<span class="p">&lt;/</span><span class="nt">nav</span><span class="p">&gt;</span>

<span class="p">&lt;</span><span class="nt">div</span> <span class="na">class</span><span class="o">=</span><span class="s">"container"</span><span class="p">&gt;</span>
    <span class="p">&lt;</span><span class="nt">h1</span><span class="p">&gt;</span> CircleCI Spring Demo <span class="p">&lt;/</span><span class="nt">h1</span><span class="p">&gt;</span>
<span class="p">&lt;/</span><span class="nt">div</span><span class="p">&gt;</span>

<span class="p">&lt;</span><span class="nt">script</span> <span class="na">th:src</span><span class="o">=</span><span class="s">"@{/webjars/bootstrap/3.3.7/js/bootstrap.min.js}"</span><span class="p">&gt;&lt;/</span><span class="nt">script</span><span class="p">&gt;</span>



</body>
</html>

However, when I tried to load up the app with mvn spring-boot:run none of the styles showed up and console showed the following error message: 
Resource interpreted as Stylesheet but transferred with MIME type text/html
It turns out, that a default spring-security config will basically block any request unless you whitelist it. The MIME type is a red herring since what is actually happening is that my spring-security config is redirecting all unauthenticated users to my login page (which is login.html) instead of serving up the stylesheet from the/webjars directory. The solution is to update my security configuration to whitelist anything that comes from /webjars 
package com.circleci.demojavaspring;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.security.config.annotation.authentication.builders.AuthenticationManagerBuilder;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.config.annotation.web.configuration.WebSecurityConfigurerAdapter;
import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;


@Configuration
@EnableWebSecurity
public class WebSecurityConfig extends WebSecurityConfigurerAdapter {
@Override
protected void configure(HttpSecurity http) throws Exception {
http
.authorizeRequests()
.antMatchers("/", "/home", "/webjars/**").permitAll()
.anyRequest().authenticated()
.and()
.formLogin()
.loginPage("/login")
.permitAll()
.and()
.logout()
.permitAll();
}
}

Now, the styles load as expected.

Thank you for reading! Share your thoughts with me on bluesky, mastodon, or via email.

Check out some more stuff to read down below.

Most popular posts this month

Recent Favorite Blog Posts

This is a collection of the last 8 posts that I bookmarked.

Articles from blogs I follow around the net

Artificial Unintelligence – We are so inured to using AI that we believe we need it

Before people around the world were connected by the internet the proliferation of new ideas and modern technologies was slow. This was bad for the originators who had no means of quickly gauging…

via V.H. Belvadi June 1, 2025

How often do LLMs snitch? Recreating Theo's SnitchBench with LLM

A fun new benchmark just dropped! Inspired by the Claude 4 system card - which showed that Claude 4 might just rat you out to the authorities if you told it to "take initiative" in enforcing its morals values while exposing it to evidence of malfe…

via Simon Willison's Weblog: Entries May 31, 2025

OpenAI featured chatbot is pushing extreme surgeries to “subhuman” men

OpenAI's featured chatbot recommends $200,000 in surgeries while promoting incel ideology

via Citation Needed May 31, 2025

Generated by openring