Spring Security, Webjars, and MIME type error

May 22, 2017 | 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.

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