Securing REST API using custom tokens (stateless, no UI, no cookies, no basic authentication, no OAuth, no login page)

Question

There are lots of guidelines, sample codes that show how to secure REST API with Spring Security, but most of them assume a web client and talk about login page, redirection

Answer 1

You're right, it isn't easy and there aren't many good examples out there. Examples i saw made it so you couldn't use other spring security stuff side by side. I did something similar recently, here's what i did.

You need a custom token to hold your header value

public class CustomToken extends AbstractAuthenticationToken {
  private final String value;

  //Getters and Constructor.  Make sure getAutheticated returns false at first.
  //I made mine "immutable" via:

      @Override
public void setAuthenticated(boolean isAuthenticated) {
    //It doesn't make sense to let just anyone set this token to authenticated, so we block it
    //Similar precautions are taken in other spring framework tokens, EG: UsernamePasswordAuthenticationToken
    if (isAuthenticated) {

        throw new IllegalArgumentException(MESSAGE_CANNOT_SET_AUTHENTICATED);
    }

    super.setAuthenticated(false);
}
}

You need a spring security filter to extract the header and ask the manager to authenticate it, something like thisemphasized text

public class CustomFilter extends AbstractAuthenticationProcessingFilter {


    public CustomFilter(RequestMatcher requestMatcher) {
        super(requestMatcher);

        this.setAuthenticationSuccessHandler((request, response, authentication) -> {
        /*
         * On success the desired action is to chain through the remaining filters.
         * Chaining is not possible through the success handlers, because the chain is not accessible in this method.
         * As such, this success handler implementation does nothing, and chaining is accomplished by overriding the successfulAuthentication method as per:
         * http://docs.spring.io/autorepo/docs/spring-security/3.2.4.RELEASE/apidocs/org/springframework/security/web/authentication/AbstractAuthenticationProcessingFilter.html#successfulAuthentication(javax.servlet.http.HttpServletRequest,%20javax.servlet.http.HttpServletResponse,%20javax.servlet.FilterChain,%20org.springframework.security.core.Authentication)
         * "Subclasses can override this method to continue the FilterChain after successful authentication."
         */
        });

    }



    @Override
    public Authentication attemptAuthentication(HttpServletRequest request, HttpServletResponse response)
            throws AuthenticationException, IOException, ServletException {


        String tokenValue = request.getHeader("SOMEHEADER");

        if(StringUtils.isEmpty(tokenValue)) {
            //Doing this check is kinda dumb because we check for it up above in doFilter
            //..but this is a public method and we can't do much if we don't have the header
            //also we can't do the check only here because we don't have the chain available
           return null;
        }


        CustomToken token = new CustomToken(tokenValue);
        token.setDetails(authenticationDetailsSource.buildDetails(request));

        return this.getAuthenticationManager().authenticate(token);
    }



    /*
     * Overriding this method to maintain the chaining on authentication success.
     * http://docs.spring.io/autorepo/docs/spring-security/3.2.4.RELEASE/apidocs/org/springframework/security/web/authentication/AbstractAuthenticationProcessingFilter.html#successfulAuthentication(javax.servlet.http.HttpServletRequest,%20javax.servlet.http.HttpServletResponse,%20javax.servlet.FilterChain,%20org.springframework.security.core.Authentication)
     * "Subclasses can override this method to continue the FilterChain after successful authentication."
     */
    @Override
    protected void successfulAuthentication(HttpServletRequest request, HttpServletResponse response, FilterChain chain, Authentication authResult) throws IOException, ServletException {


        //if this isn't called, then no auth is set in the security context holder
        //and subsequent security filters can still execute.  
        //so in SOME cases you might want to conditionally call this
        super.successfulAuthentication(request, response, chain, authResult);

        //Continue the chain
        chain.doFilter(request, response);

    }


}

Register your custom filter in spring security chain

 @Configuration
 public static class ResourceEndpointsSecurityConfig extends WebSecurityConfigurerAdapter {        

      //Note, we don't register this as a bean as we don't want it to be added to the main Filter chain, just the spring security filter chain
      protected AbstractAuthenticationProcessingFilter createCustomFilter() throws Exception {
        CustomFilter filter = new CustomFilter( new RegexRequestMatcher("^/.*", null));
        filter.setAuthenticationManager(this.authenticationManagerBean());
        return filter;
      }

       @Override
       protected void configure(HttpSecurity http) throws Exception {                  

            http
            //fyi: This adds it to the spring security proxy filter chain
            .addFilterBefore(createCustomFilter(), AnonymousAuthenticationFilter.class)
       }
}

A custom auth provider to validate that token extracted with the filter.

public class CustomAuthenticationProvider implements AuthenticationProvider {


    @Override
    public Authentication authenticate(Authentication auth)
            throws AuthenticationException {

        CustomToken token = (CustomToken)auth;

        try{
           //Authenticate token against redis or whatever you want

            //This i found weird, you need a Principal in your Token...I use User
            //I found this to be very redundant in spring security, but Controller param resolving will break if you don't do this...anoying
            org.springframework.security.core.userdetails.User principal = new User(...); 

            //Our token resolved to a username so i went with this token...you could make your CustomToken take the principal.  getCredentials returns "NO_PASSWORD"..it gets cleared out anyways.  also the getAuthenticated for the thing you return should return true now
            return new UsernamePasswordAuthenticationToken(principal, auth.getCredentials(), principal.getAuthorities());
        } catch(Expection e){
            //TODO throw appropriate AuthenticationException types
            throw new BadCredentialsException(MESSAGE_AUTHENTICATION_FAILURE, e);
        }


    }

    @Override
    public boolean supports(Class authentication) {
        return CustomToken.class.isAssignableFrom(authentication);
    }


}

Finally, register your provider as a bean so the authentication manager finds it in some @Configuration class. You probably could just @Component it too, i prefer this method

@Bean
public AuthenticationProvider createCustomAuthenticationProvider(injectedDependencies)  {
    return new CustomAuthenticationProvider(injectedDependencies);
}