Documentation
Middlewares
Surf

Surf

Basic CSRF protection middleware for Ambiorix

When a request comes in (it ignores GET, HEAD, and OPTIONS) it checks for the presence of a token. It looks for said token in the following places, in that order:

  • _csrf in the body of the response (e.g.: what was POSTed, see form example below), both JSON and multipart.
  • The query for _csrf value (?_csrf=token)
  • Header csrf-token
  • Header xsrf-token
  • Header x-csrf-token
  • Header x-xsrf-token

Where you need this token it can be retrieved with req$csrf_token.

Installation

# install.packages("remotes")
remotes::install_github("surf")

Example

Valid

library(surf)
library(ambiorix)

app <- Ambiorix$new()

# use the middleware
app$use(surf())

app$get("/", \(req, res){
  res$sendf(
    "<h1>What's your name?</h1>
    <form action='/' method='POST' enctype='multipart/form-data'>
      <input type='hidden' name='_csrf' value='%s' />
      <input type='text' name='name' />
      <input type='submit' value='send'/>
    </form>",
    req$csrf_token() # get token
  )
})

app$post("/", \(req, res) {
  body <- req$parse_multipart()
  res$sendf("Hi %s", body$name)
})

app$start()

Invalid

library(surf)
library(ambiorix)

app <- Ambiorix$new()

# use the middleware
app$use(surf())

app$get("/", \(req, res){
  # missing CSRF token
  res$send(
    "<h1>What's your name?</h1>
    <form action='/' method='POST' enctype='multipart/form-data'>
      <input type='text' name='name' />
      <input type='submit' value='send'/>
    </form>"
  )
})

app$post("/", \(req, res) {
  body <- req$parse_multipart()
  res$sendf("Hi %s", body$name)
})

app$start()