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github.com/gorilla/csrf

Package csrf (gorilla/csrf) provides Cross Site Request Forgery (CSRF) prevention middleware for Go web applications & services. It includes: * The `csrf.Protect` middleware/handler provides CSRF protection on routes attached to a router or a sub-router. * A `csrf.Token` function that provides the token to pass into your response, whether that be a HTML form or a JSON response body. * ... and a `csrf.TemplateField` helper that you can pass into your `html/template` templates to replace a `{{ .csrfField }}` template tag with a hidden input field. gorilla/csrf is easy to use: add the middleware to individual handlers with the below: ... and then collect the token with `csrf.Token(r)` before passing it to the template, JSON body or HTTP header (you pick!). gorilla/csrf inspects the form body (first) and HTTP headers (second) on subsequent POST/PUT/PATCH/DELETE/etc. requests for the token. Note that the authentication key passed to `csrf.Protect([]byte(key))` should be 32-bytes long and persist across application restarts. Generating a random key won't allow you to authenticate existing cookies and will break your CSRF validation. Here's the common use-case: HTML forms you want to provide CSRF protection for, in order to protect malicious POST requests being made: Note that the CSRF middleware will (by necessity) consume the request body if the token is passed via POST form values. If you need to consume this in your handler, insert your own middleware earlier in the chain to capture the request body. You can also send the CSRF token in the response header. This approach is useful if you're using a front-end JavaScript framework like Ember or Angular, or are providing a JSON API: If you're writing a client that's supposed to mimic browser behavior, make sure to send back the CSRF cookie (the default name is _gorilla_csrf, but this can be changed with the CookieName Option) along with either the X-CSRF-Token header or the gorilla.csrf.Token form field. In addition: getting CSRF protection right is important, so here's some background: * This library generates unique-per-request (masked) tokens as a mitigation against the BREACH attack (http://breachattack.com/). * The 'base' (unmasked) token is stored in the session, which means that multiple browser tabs won't cause a user problems as their per-request token is compared with the base token. * Operates on a "whitelist only" approach where safe (non-mutating) HTTP methods (GET, HEAD, OPTIONS, TRACE) are the *only* methods where token validation is not enforced. * The design is based on the battle-tested Django (https://docs.djangoproject.com/en/1.8/ref/csrf/) and Ruby on Rails (http://api.rubyonrails.org/classes/ActionController/RequestForgeryProtection.html) approaches. * Cookies are authenticated and based on the securecookie (https://github.com/gorilla/securecookie) library. They're also Secure (issued over HTTPS only) and are HttpOnly by default, because sane defaults are important. * Go's `crypto/rand` library is used to generate the 32 byte (256 bit) tokens and the one-time-pad used for masking them. This library does not seek to be adventurous.

    v1.7.2

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# gorilla/csrf

![testing](https://github.com/gorilla/csrf/actions/workflows/test.yml/badge.svg)
[![codecov](https://codecov.io/github/gorilla/csrf/branch/main/graph/badge.svg)](https://codecov.io/github/gorilla/csrf)
[![godoc](https://godoc.org/github.com/gorilla/csrf?status.svg)](https://godoc.org/github.com/gorilla/csrf)
[![sourcegraph](https://sourcegraph.com/github.com/gorilla/csrf/-/badge.svg)](https://sourcegraph.com/github.com/gorilla/csrf?badge)


![Gorilla Logo](https://github.com/gorilla/.github/assets/53367916/d92caabf-98e0-473e-bfbf-ab554ba435e5)

gorilla/csrf is a HTTP middleware library that provides [cross-site request
forgery](http://blog.codinghorror.com/preventing-csrf-and-xsrf-attacks/) (CSRF)
protection. It includes:

- The `csrf.Protect` middleware/handler provides CSRF protection on routes
  attached to a router or a sub-router.
- A `csrf.Token` function that provides the token to pass into your response,
  whether that be a HTML form or a JSON response body.
- ... and a `csrf.TemplateField` helper that you can pass into your `html/template`
  templates to replace a `{{ .csrfField }}` template tag with a hidden input
  field.

gorilla/csrf is designed to work with any Go web framework, including:

- The [Gorilla](https://www.gorillatoolkit.org/) toolkit
- Go's built-in [net/http](http://golang.org/pkg/net/http/) package
- [Goji](https://goji.io) - see the [tailored fork](https://github.com/goji/csrf)
- [Gin](https://github.com/gin-gonic/gin)
- [Echo](https://github.com/labstack/echo)
- ... and any other router/framework that rallies around Go's `http.Handler` interface.

gorilla/csrf is also compatible with middleware 'helper' libraries like
[Alice](https://github.com/justinas/alice) and [Negroni](https://github.com/codegangsta/negroni).

## Contents

  * [Install](#install)
  * [Examples](#examples)
    + [HTML Forms](#html-forms)
    + [JavaScript Applications](#javascript-applications)
    + [Google App Engine](#google-app-engine)
    + [Setting SameSite](#setting-samesite)
    + [Setting Options](#setting-options)
  * [Design Notes](#design-notes)
  * [License](#license)

## Install

With a properly configured Go toolchain:

```sh
go get github.com/gorilla/csrf
```

## Examples

- [HTML Forms](#html-forms)
- [JavaScript Apps](#javascript-applications)
- [Google App Engine](#google-app-engine)
- [Setting SameSite](#setting-samesite)
- [Setting Options](#setting-options)

gorilla/csrf is easy to use: add the middleware to your router with
the below:

```go
CSRF := csrf.Protect([]byte("32-byte-long-auth-key"))
http.ListenAndServe(":8000", CSRF(r))
```

...and then collect the token with `csrf.Token(r)` in your handlers before
passing it to the template, JSON body or HTTP header (see below).

Note that the authentication key passed to `csrf.Protect([]byte(key))` should:
- be 32-bytes long
- persist across application restarts.
- kept secret from potential malicious users - do not hardcode it into the source code, especially not in open-source applications.

Generating a random key won't allow you to authenticate existing cookies and will break your CSRF
validation.

gorilla/csrf inspects the HTTP headers (first) and form body (second) on
subsequent POST/PUT/PATCH/DELETE/etc. requests for the token.

### HTML Forms

Here's the common use-case: HTML forms you want to provide CSRF protection for,
in order to protect malicious POST requests being made:

```go
package main

import (
    "net/http"

    "github.com/gorilla/csrf"
    "github.com/gorilla/mux"
)

func main() {
    r := mux.NewRouter()
    r.HandleFunc("/signup", ShowSignupForm)
    // All POST requests without a valid token will return HTTP 403 Forbidden.
    // We should also ensure that our mutating (non-idempotent) handler only
    // matches on POST requests. We can check that here, at the router level, or
    // within the handler itself via r.Method.
    r.HandleFunc("/signup/post", SubmitSignupForm).Methods("POST")

    // Add the middleware to your router by wrapping it.
    http.ListenAndServe(":8000",
        csrf.Protect([]byte("32-byte-long-auth-key"))(r))
    // PS: Don't forget to pass csrf.Secure(false) if you're developing locally
    // over plain HTTP (just don't leave it on in production).
}

func ShowSignupForm(w http.ResponseWriter, r *http.Request) {
    // signup_form.tmpl just needs a {{ .csrfField }} template tag for
    // csrf.TemplateField to inject the CSRF token into. Easy!
    t.ExecuteTemplate(w, "signup_form.tmpl", map[string]interface{}{
        csrf.TemplateTag: csrf.TemplateField(r),
    })
    // We could also retrieve the token directly from csrf.Token(r) and
    // set it in the request header - w.Header.Set("X-CSRF-Token", token)
    // This is useful if you're sending JSON to clients or a front-end JavaScript
    // framework.
}

func SubmitSignupForm(w http.ResponseWriter, r *http.Request) {
    // We can trust that requests making it this far have satisfied
    // our CSRF protection requirements.
}
```

Note that the CSRF middleware will (by necessity) consume the request body if the
token is passed via POST form values. If you need to consume this in your
handler, insert your own middleware earlier in the chain to capture the request
body.

### JavaScript Applications

This approach is useful if you're using a front-end JavaScript framework like
React, Ember or Angular, and are providing a JSON API. Specifically, we need
to provide a way for our front-end fetch/AJAX calls to pass the token on each
fetch (AJAX/XMLHttpRequest) request. We achieve this by:

- Parsing the token from the `<input>` field generated by the
  `csrf.TemplateField(r)` helper, or passing it back in a response header.
- Sending this token back on every request
- Ensuring our cookie is attached to the request so that the form/header
  value can be compared to the cookie value.

We'll also look at applying selective CSRF protection using
[gorilla/mux's](https://www.gorillatoolkit.org/pkg/mux) sub-routers,
as we don't handle any POST/PUT/DELETE requests with our top-level router.

```go
package main

import (
    "github.com/gorilla/csrf"
    "github.com/gorilla/mux"
)

func main() {
    r := mux.NewRouter()
    csrfMiddleware := csrf.Protect([]byte("32-byte-long-auth-key"))

    api := r.PathPrefix("/api").Subrouter()
    api.Use(csrfMiddleware)
    api.HandleFunc("/user/{id}", GetUser).Methods("GET")

    http.ListenAndServe(":8000", r)
}

func GetUser(w http.ResponseWriter, r *http.Request) {
    // Authenticate the request, get the id from the route params,
    // and fetch the user from the DB, etc.

    // Get the token and pass it in the CSRF header. Our JSON-speaking client
    // or JavaScript framework can now read the header and return the token in
    // in its own "X-CSRF-Token" request header on the subsequent POST.
    w.Header().Set("X-CSRF-Token", csrf.Token(r))
    b, err := json.Marshal(user)
    if err != nil {
        http.Error(w, err.Error(), 500)
        return
    }

    w.Write(b)
}
```

In our JavaScript application, we should read the token from the response
headers and pass it in a request header for all requests. Here's what that
looks like when using [Axios](https://github.com/axios/axios), a popular
JavaScript HTTP client library:

```js
// You can alternatively parse the response header for the X-CSRF-Token, and
// store that instead, if you followed the steps above to write the token to a
// response header.
let csrfToken = document.getElementsByName("gorilla.csrf.Token")[0].value

// via https://github.com/axios/axios#creating-an-instance
const instance = axios.create({
  baseURL: "https://example.com/api/",
  timeout: 1000,
  headers: { "X-CSRF-Token": csrfToken }
})

// Now, any HTTP request you make will include the csrfToken from the page,
// provided you update the csrfToken variable for each render.
try {
  let resp = await instance.post(endpoint, formData)
  // Do something with resp
} catch (err) {
  // Handle the exception
}
```

If you plan to host your JavaScript application on another domain, you can use the Trusted Origins
feature to allow the host of your JavaScript application to make requests to your Go application. Observe the example below:


```go
package main

import (
    "github.com/gorilla/csrf"
    "github.com/gorilla/mux"
)

func main() {
    r := mux.NewRouter()
    csrfMiddleware := csrf.Protect([]byte("32-byte-long-auth-key"), csrf.TrustedOrigins([]string{"ui.domain.com"}))

    api := r.PathPrefix("/api").Subrouter()
    api.Use(csrfMiddleware)
    api.HandleFunc("/user/{id}", GetUser).Methods("GET")

    http.ListenAndServe(":8000", r)
}

func GetUser(w http.ResponseWriter, r *http.Request) {
    // Authenticate the request, get the id from the route params,
    // and fetch the user from the DB, etc.

    // Get the token and pass it in the CSRF header. Our JSON-speaking client
    // or JavaScript framework can now read the header and return the token in
    // in its own "X-CSRF-Token" request header on the subsequent POST.
    w.Header().Set("X-CSRF-Token", csrf.Token(r))
    b, err := json.Marshal(user)
    if err != nil {
        http.Error(w, err.Error(), 500)
        return
    }

    w.Write(b)
}
```

On the example above, you're authorizing requests from `ui.domain.com` to make valid CSRF requests to your application, so you can have your API server on another domain without problems.

### Google App Engine

If you're using [Google App
Engine](https://cloud.google.com/appengine/docs/go/how-requests-are-handled#Go_Requests_and_HTTP),
(first-generation) which doesn't allow you to hook into the default `http.ServeMux` directly,
you can still use gorilla/csrf (and gorilla/mux):

```go
package app

// Remember: appengine has its own package main
func init() {
    r := mux.NewRouter()
    r.HandleFunc("/", IndexHandler)
    // ...

    // We pass our CSRF-protected router to the DefaultServeMux
    http.Handle("/", csrf.Protect([]byte(your-key))(r))
}
```

Note: You can ignore this if you're using the
[second-generation](https://cloud.google.com/appengine/docs/go/) Go runtime
on App Engine (Go 1.11 and above).

### Setting SameSite

Go 1.11 introduced the option to set the SameSite attribute in cookies. This is
valuable if a developer wants to instruct a browser to not include cookies during
a cross site request. SameSiteStrictMode prevents all cross site requests from including
the cookie. SameSiteLaxMode prevents CSRF prone requests (POST) from including the cookie
but allows the cookie to be included in GET requests to support external linking.

```go
func main() {
    CSRF := csrf.Protect(
      []byte("a-32-byte-long-key-goes-here"),
      // instruct the browser to never send cookies during cross site requests
      csrf.SameSite(csrf.SameSiteStrictMode),
    )

    r := mux.NewRouter()
    r.HandleFunc("/signup", GetSignupForm)
    r.HandleFunc("/signup/post", PostSignupForm)

    http.ListenAndServe(":8000", CSRF(r))
}
```

### Cookie path

By default, CSRF cookies are set on the path of the request.

This can create issues, if the request is done from one path to a different path.

You might want to set up a root path for all the cookies; that way, the CSRF will always work across all your paths.

```
    CSRF := csrf.Protect(
      []byte("a-32-byte-long-key-goes-here"),
      csrf.Path("/"),
    )
```

### Setting Options

What about providing your own error handler and changing the HTTP header the
package inspects on requests? (i.e. an existing API you're porting to Go). Well,
gorilla/csrf provides options for changing these as you see fit:

```go
func main() {
    CSRF := csrf.Protect(
            []byte("a-32-byte-long-key-goes-here"),
            csrf.RequestHeader("Authenticity-Token"),
            csrf.FieldName("authenticity_token"),
            csrf.ErrorHandler(http.HandlerFunc(serverError(403))),
    )

    r := mux.NewRouter()
    r.HandleFunc("/signup", GetSignupForm)
    r.HandleFunc("/signup/post", PostSignupForm)

    http.ListenAndServe(":8000", CSRF(r))
}
```

Not too bad, right?

If there's something you're confused about or a feature you would like to see
added, open an issue.

## Design Notes

Getting CSRF protection right is important, so here's some background:

- This library generates unique-per-request (masked) tokens as a mitigation
  against the [BREACH attack](http://breachattack.com/).
- The 'base' (unmasked) token is stored in the session, which means that
  multiple browser tabs won't cause a user problems as their per-request token
  is compared with the base token.
- Operates on a "whitelist only" approach where safe (non-mutating) HTTP methods
  (GET, HEAD, OPTIONS, TRACE) are the _only_ methods where token validation is not
  enforced.
- The design is based on the battle-tested
  [Django](https://docs.djangoproject.com/en/1.8/ref/csrf/) and [Ruby on
  Rails](http://api.rubyonrails.org/classes/ActionController/RequestForgeryProtection.html)
  approaches.
- Cookies are authenticated and based on the [securecookie](https://github.com/gorilla/securecookie)
  library. They're also Secure (issued over HTTPS only) and are HttpOnly
  by default, because sane defaults are important.
- Cookie SameSite attribute (prevents cookies from being sent by a browser
  during cross site requests) are not set by default to maintain backwards compatibility
  for legacy systems. The SameSite attribute can be set with the SameSite option.
- Go's `crypto/rand` library is used to generate the 32 byte (256 bit) tokens
  and the one-time-pad used for masking them.

This library does not seek to be adventurous.

## License

BSD licensed. See the LICENSE file for details.

FAQs

Last updated on 05 Nov 2023

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