code: protected void addRequestHeaders(final HttpServletRequest httpServletRequest, final Map<String, List<Object>> attributes) {
          for (final Map.Entry<String, Set<String>> headerAttributeEntry : this.headerAttributeMapping.entrySet()) {
              final String headerName = headerAttributeEntry.getKey();
              final String value = httpServletRequest.getHeader(headerName);
  
              if (value != null) {
                  for (final String attributeName : headerAttributeEntry.getValue()) {
                      attributes.put(attributeName,
                              headersToIgnoreSemicolons.contains(headerName) ?
                                      list(value)
                                      : splitOnSemiColonHandlingBackslashEscaping(value));
                  }
              }
          }
      }
docs: Add request headers to the attributes map
  
  @param httpServletRequest Http Servlet Request
  @param attributes Map of attributes to add additional attributes to from the Http Request