JWTAuthenticationFilter.java

public class JWTAuthenticationFilter extends GenericFilterBean {
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse,
                         FilterChain filterChain) throws IOException, ServletException {
        Authentication auth = TokenAuthenticationService.getAuth((HttpServletRequest) servletRequest);
        SecurityContextHolder.getContext().setAuthentication(auth);
        filterChain.doFilter(servletRequest, servletResponse);
    }
    
   static Authentication getAuthentication(HttpServletRequest request) {
    String token = request.getHeader(HEADER_STRING);
    if (token != null) {
      // parse the token.
      String user = Jwts.parser()
          .setSigningKey(SECRET)
          .parseClaimsJws(token.replace(TOKEN_PREFIX, ""))
          .getBody()
          .getSubject();

      return user != null ?
          new UsernamePasswordAuthenticationToken(user, null, emptyList()) :
          null;
    }
    return null;
  }
}