https://kb.jarylchng.com/i/n8n-and-authelia-bypass-n8n-native-login-page-usin-sNRmS-7j5u1/

n8n_authelia_hooks.js

const { dirname, resolve } = require('path')
const Layer = require('express/lib/router/layer')
const { issueCookie } = require(resolve(dirname(require.resolve('n8n')), 'auth/jwt'))
const ignoreAuthRegexp = /^\/(assets|healthz|webhook|rest\/oauth2-credential)/
module.exports = {
    n8n: {
        ready: [
            async function ({ app }, config) {
                const { stack } = app._router
                const index = stack.findIndex((l) => l.name === 'cookieParser')
                stack.splice(index + 1, 0, new Layer('/', {
                    strict: false,
                    end: false
                }, async (req, res, next) => {
                    // skip if URL is ignored
                    if (ignoreAuthRegexp.test(req.url)) return next()

                    // skip if user management is not set up yet
                    if (!config.get('userManagement.isInstanceOwnerSetUp', false)) return next()

                    // skip if cookie already exists
                    if (req.cookies?.['n8n-auth']) return next()

                    // if N8N_FORWARD_AUTH_HEADER is not set, skip
                    if (!process.env.N8N_FORWARD_AUTH_HEADER) return next()

                    // if N8N_FORWARD_AUTH_HEADER header is not found, skip
                    const email = req.headers[process.env.N8N_FORWARD_AUTH_HEADER.toLowerCase()]
                    if (!email) return next()

                    // search for user with email
                    const user = await this.dbCollections.User.findOneBy({email})
                    if (!user) {
                        res.statusCode = 401
                        res.end(`User ${email} not found, please have an admin invite the user first.`)
                        return
                    }

                    // issue cookie if all is OK
                    issueCookie(res, user)
                    return next()
                }))
            },
        ],
    },
}