Axios CSRF header configuration doesn't work

[Mado13]

Description

When using Inertia.js with Phoenix, setting axios.defaults.xsrfHeaderName doesn't affect the CSRF header sent with Inertia requests.

Problem

According to the documentation, setting axios.defaults.xsrfHeaderName = "x-csrf-token" should configure Axios to send the CSRF token with the header name that Phoenix expects. However, Inertia continues to send the token as x-xsrf-token instead, causing Phoenix's CSRF protection to reject the requests

Reproduction Steps

Configure Axios in app.js:

import axios from "axios";
axios.defaults.xsrfHeaderName = "x-csrf-token";

Initialize Inertia app as normal
Submit a form using Inertia's useForm to a Phoenix endpoint
Observe in the network tab that the request includes x-xsrf-token header but not x-csrf-token

Expected Behavior

The CSRF token should be sent with the x-csrf-token header as configured in the Axios defaults.

Actual Behavior

The CSRF token is sent with the x-xsrf-token header regardless of the Axios configuration.

Workaround

I was able to work around this issue by intercepting Inertia's requests and manually changing the header:

Inertia.on('before', (event) => {
  const getCookieValue = (name) => {
    const cookies = document.cookie.split('; ');
    for (const cookie of cookies) {
      const [cookieName, cookieValue] = cookie.split('=');
      if (cookieName === name) {
        return decodeURIComponent(cookieValue);
      }
    }
    return null;
  };

  const token = getCookieValue('XSRF-TOKEN');
  
  if (token) {
    event.detail.visit.headers['x-csrf-token'] = token;
    delete event.detail.visit.headers['x-xsrf-token'];
  }
});

Environment

Inertia.js: 2.3.0
Phoenix: 1.7.0
Svelte: 5

[derrickreimer]

Hmm that's odd! This is not what I'm seeing in my applications using the Axios defaults overrides (though I'm typically using React and not Svelte). Can you share a bit more of your app.js setup?

[Mado13]

Yeah sure this is it!

import axios from "axios";
import { createInertiaApp } from "@inertiajs/svelte";
import { Inertia } from "@inertiajs/inertia";
import { mount, hydrate } from "svelte";
import { register, init, getLocaleFromNavigator, locale } from 'svelte-i18n';
import "phoenix_html";
import { setupPWA } from "./pwa-setup";
import '../styles/global.scss';
import Layout from './Layout.svelte'

// Initialize application state
window.pwa = {};
window.isPWAInstalled = false;

// Configure i18n (internationalization)
const setupI18n = () => {
  // Register language packs
  register('en', () => import('../lang/en.json'));
  register('he', () => import('../lang/he.json'));
  
  // Initialize with browser's preferred language, with a fallback
  init({
    fallbackLocale: 'he',
    initialLocale: 'he',
  });

  locale.subscribe((lang) => {
    console.log(`Setting language to ${lang}, direction: ${lang === 'he' ? 'rtl' : 'ltr'}`);
    document.documentElement.dir = lang === 'he' ? 'rtl' : 'ltr';
    document.documentElement.lang = lang;
  });
  
  return new Promise((resolve) => {
    const unsubscribe = locale.subscribe((lang) => {
      if (lang) {
        document.documentElement.dir = lang === 'he' ? 'rtl' : 'ltr';
        document.documentElement.lang = lang;
        unsubscribe();
        resolve();
      }
    });
    
    setTimeout(() => {
      locale.set('he');
    }, 100);
  });
};

// Configure HTTP requests
const configureAxios = () => {
  axios.defaults.xsrfHeaderName = "x-csrf-token";
  
  // Add CSRF token to Inertia requests
  Inertia.on('before', (event) => {
    const token = getCookieValue('XSRF-TOKEN');
    
    if (token) {
      event.detail.visit.headers['x-csrf-token'] = token;
      delete event.detail.visit.headers['x-xsrf-token']; // Remove incorrect header
    }
  });
};

const getCookieValue = (name) => {
  const cookies = document.cookie.split('; ');
  for (const cookie of cookies) {
    const [cookieName, cookieValue] = cookie.split('=');
    if (cookieName === name) {
      return decodeURIComponent(cookieValue);
    }
  }
  return null;
};

// Initialize Inertia application
const initApp = () => {
  createInertiaApp({
    // Resolve page components
    resolve: name => {
      const pages = import.meta.glob('./Pages/**/*.svelte', { eager: true })
      let page = pages[`./Pages/${name}.svelte`]
      return { default: page.default, layout: page.layout || Layout }
    },
    
    // Mount the application
    setup({ el, App, props }) {
      const enhancedProps = {
        ...props,
        pwaInstalled: window.isPWAInstalled ?? false,
      };
      
      // Use hydration for server-rendered content, otherwise mount
      if (el.dataset.serverRendered === 'true') {
        hydrate(App, { target: el, props: enhancedProps });
      } else {
        mount(App, { target: el, props: enhancedProps });
      }
    },
  });
};

// Application bootstrap
const bootstrap = async () => {
  await setupI18n();
  configureAxios();
  initApp();
  setupPWA();
};

// Start the application
bootstrap().catch(err => console.error('Bootstrap error:', err));