express-basic-auth

Simple plug & play HTTP basic auth middleware for Express.

How to install

Just run

npm install express-basic-auth

How to use

The module will export a function, that you can call with an options object toget the middleware:

const app = require('express')()
const basicAuth = require('express-basic-auth')

app.use(basicAuth({
    users: { 'admin': 'supersecret' }
}))

The middleware will now check incoming requests to match the credentialsadmin:supersecret.

The middleware will check incoming requests for a basic auth (Authorization)header, parse it and check if the credentials are legit. If there are anycredentials, an auth property will be added to the request, containingan object with user and password properties, filled with the credentials,no matter if they are legit or not.

If a request is found to not be authorized, it will respond with HTTP 401and a configurable body (default empty).

Static Users

If you simply want to check basic auth against one or multiple static credentials,you can pass those credentials in the users option:

app.use(basicAuth({
    users: {
        'admin': 'supersecret',
        'adam': 'password1234',
        'eve': 'asdfghjkl',
    }
}))

The middleware will check incoming requests to have a basic auth header matchingone of the three passed credentials.

Custom authorization

Alternatively, you can pass your own authorizer function, to check the credentialshowever you want. It will be called with a username and password and is expected toreturn true or false to indicate that the credentials were approved or not.

When using your own authorizer, make sure not to use standard string comparison (== / ===)when comparing user input with secret credentials, as that would make you vulnerable againsttiming attacks. Use the provided safeComparefunction instead - always provide the user input as its first argument. Also make sure to use bitwiselogic operators (| and &) instead of the standard ones (|| and &&) for the same reason, asthe standard ones use shortcuts.

app.use(basicAuth( { authorizer: myAuthorizer } ))

function myAuthorizer(username, password) {
    const userMatches = basicAuth.safeCompare(username, 'customuser')
    const passwordMatches = basicAuth.safeCompare(password, 'custompassword')

    return userMatches & passwordMatches
}

This will authorize all requests with the credentials 'customuser:custompassword'.In an actual application you would likely look up some data instead ;-) You can do whatever youwant in custom authorizers, just return true or false in the end and stay aware of timingattacks.

Custom Async Authorization

Note that the authorizer function above is expected to be synchronous. This isthe default behavior, you can pass authorizeAsync: true in the options object to indicatethat your authorizer is asynchronous. In this case it will be passed a callbackas the third parameter, which is expected to be called by standard node conventionwith an error and a boolean to indicate if the credentials have been approved or not.Let's look at the same authorizer again, but this time asynchronous:

app.use(basicAuth({
    authorizer: myAsyncAuthorizer,
    authorizeAsync: true,
}))

function myAsyncAuthorizer(username, password, cb) {
    if (username.startsWith('A') & password.startsWith('secret'))
        return cb(null, true)
    else
        return cb(null, false)
}

Unauthorized Response Body

Per default, the response body for unauthorized responses will be empty. It canbe configured using the unauthorizedResponse option. You can either pass astatic response or a function that gets passed the express request object and isexpected to return the response body. If the response body is a string, it willbe used as-is, otherwise it will be sent as JSON:

app.use(basicAuth({
    users: { 'Foo': 'bar' },
    unauthorizedResponse: getUnauthorizedResponse
}))

function getUnauthorizedResponse(req) {
    return req.auth
        ? ('Credentials ' + req.auth.user + ':' + req.auth.password + ' rejected')
        : 'No credentials provided'
}

Challenge

Per default the middleware will not add a WWW-Authenticate challenge header toresponses of unauthorized requests. You can enable that by adding challenge: trueto the options object. This will cause most browsers to show a popup to entercredentials on unauthorized responses. You can set the realm (the realmidentifies the system to authenticate against and can be used by clients to savecredentials) of the challenge by passing a static string or a function that getspassed the request object and is expected to return the challenge:

app.use(basicAuth({
    users: { 'someuser': 'somepassword' },
    challenge: true,
    realm: 'Imb4T3st4pp',
}))

Try it

The repository contains an example.js that you can run to play around and trythe middleware. To use it just put it somewhere (or leave it where it is), run

npm install express express-basic-auth
node example.js

This will start a small express server listening at port 8080. Just look at the file,try out the requests and play around with the options.

TypeScript usage

A declaration file is bundled with the library. You don't have to install a @types/ package.

import * as basicAuth from 'express-basic-auth'

�� Using req.auth

express-basic-auth sets req.auth to an object containing the authorized credentials like { user: 'admin', password: 'supersecret' }.

In order to use that req.auth property in TypeScript without an unknown property error, use covariance to downcast the request type:

app.use(basicAuth(options), (req: basicAuth.IBasicAuthedRequest, res, next) => {
    res.end(`Welcome ${req.auth.user} (your password is ${req.auth.password})`)
    next()
})

�� A note about type inference on synchronous authorizers

Due to some TypeScript's type-system limitation, the arguments' type of the synchronous authorizers are not inferred.For example, on an asynchronous authorizer, the three arguments are correctly inferred:

basicAuth({
    authorizeAsync: true,
    authorizer: (user, password, authorize) => authorize(null, password == 'secret'),
})

However, on a synchronous authorizer, you'll have to type the arguments yourself:

basicAuth({
    authorizer: (user: string, password: string) => (password == 'secret')
})

Tests

The cases in the example.js are also used for automated testing. So if you want
to contribute or just make sure that the package still works, simply run:

npm test