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https://github.com/nubank/clj-github-app

A library to implement GitHub Apps in Clojure.
https://github.com/nubank/clj-github-app

authentication client clojure github webhook

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A library to implement GitHub Apps in Clojure.

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# clj-github-app

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[![Clojars Project](https://img.shields.io/clojars/v/nubank/clj-github-app.svg)](https://clojars.org/nubank/clj-github-app)



A library to implement [GitHub Apps] in Clojure.



```clj

[nubank/clj-github-app "0.2.0"]

```



Includes:



* [Webhook payload signature checker][webhook-signatures] with [secure comparison](https://github.com/weavejester/crypto-equality).

* API client with HTTP connection pool.

* Access token manager with caching ([Authenticating with GitHub Apps] is tricky).



## Usage



### Checking webhook signatures



When implementing a webhook handler, it is recommended to check the webhook request signature before processing it.

Please read the [official documentation][webhook-signatures] first.



Imagine you have a webhook handler:



```clj

(ns your-project.webhooks

  (:require [clj-github-app.webhook-signature :as webhook-signature]))



(def GITHUB_WEBHOOK_SECRET (System/getenv "GITHUB_WEBHOOK_SECRET"))



(defn post-github

  "Checks if the webhook is valid and handles it."

  [request]

  (let [{:strs [x-github-delivery x-github-event x-hub-signature-256]} (:headers request)

        payload (slurp (:body request))]

    (case (webhook-signature/check-payload-signature-256 GITHUB_WEBHOOK_SECRET x-hub-signature-256 payload)

      ::webhook-signature/missing-signature {:status 400 :body "x-hub-signature-256 header is missing"}

      ::webhook-signature/wrong-signature {:status 401 :body "x-hub-signature-256 does not match"}

      (let [parsed-payload  (json/parse-string payload keyword)]

        ;; process your webhook here

        {:status 200 :body "This is fine."}))))

```



The key part here is the call to  `check-payload-signature-256`. It takes 3 arguments:



* `webhook-secret` — the exact secret string that you set when configuring webhook for your repo.  

    If this argument is blank or nil, `check-payload-signature-256` will do nothing and return

    `:clj-github-app.webhook-signature/not-checked`.

* `x-hub-signature-256` — contents of "X-Hub-Signature-256" request header.

* `payload` — request body as a string.



Possible return values:



* `:clj-github-app.webhook-signature/ok` — signature matches the payload.

* `:clj-github-app.webhook-signature/wrong-signature` — signature does not match the payload.

* `:clj-github-app.webhook-signature/missing-signature` — `x-hub-signature` parameter was blank or nil.

* `:clj-github-app.webhook-signature/not-checked` — no check was done because `webhook-secret` parameter was blank or nil.



### Authenticating as a GitHub App



Please read [Authenticating with GitHub Apps] official documentation first.



Example (uses [mount-lite]):



```clj

(ns your-project.external.github

  (:require [mount.lite :as m]

            [clj-github-app.client :as client]))



(def GITHUB_API_URL "https://api.github.com")

(def GITHUB_APP_ID (System/getenv "GITHUB_APP_ID"))

(def GITHUB_APP_PRIVATE_KEY_PEM (System/getenv "GITHUB_APP_PRIVATE_KEY_PEM"))



(m/defstate client

  :start (client/make-app-client GITHUB_API_URL GITHUB_APP_ID GITHUB_APP_PRIVATE_KEY_PEM {})

  :stop (.close @client))

```



`clj-github-app.client/make-app-client` takes 4 parameters:



* `github-api-url` — Base URL of GitHub API. Usually `https://api.github.com` or something like `https://github.example.com/api/v3` for GHE.

* `github-app-id` — GitHub App ID as string (can be found on the app settings page).

* `private-key-pem-str` — String contents of the private key file that you [generated when configuring the app](https://developer.github.com/apps/building-github-apps/authenticating-with-github-apps/#generating-a-private-key).

* `connection-pool-opts` — [clj-http connection pool parameters](https://github.com/dakrone/clj-http#persistent-connections).

    Can be set to `{}` to use all defaults.



It returns an object that implements `AutoCloseable` interface and `AppClient` protocol, which has the following functions:



* `request*` — to [authenticate as an installation][as-installation].

    Given `installation-id` and `opts`, makes an HTTP request to GitHub API, automatically retrieving an access token.  

    Uses [clj-http], `opts` argument is given to `request` function as described [here](https://github.com/dakrone/clj-http#raw-request).

    `opts` is supposed to include `:method` and `:url` keys.

    This function is the main workhorse.

* `request` — same as `request*`, but has separate arguments for method and URL.

* `app-request*` — to [authenticate as a GitHub App][as-app].

    This is only useful for querying app metadata.

* `app-request` — same as `app-request*`, but has separate arguments for method and URL.



You can [authenticate as a GitHub App][as-app]:



```clj

(client/app-request* @client {:method :get :url "/app" :accept "application/vnd.github.machine-man-preview+json"})

(client/app-request @client :get "/app" {:accept "application/vnd.github.machine-man-preview+json"})

```



You can also [authenticate as an installation][as-installation]. For this you need Installation ID,

(which is usually given to you in webhook payloads):



```clj

(client/request* @client 42 {:method :get :url "/repos/myname/myrepo/issues/123/comments")

(client/request @client 42 :get "/repos/myname/myrepo/issues/123/comments" {})

```



All these functions can accept either a full URL or just a relative path, which will be automatically appended to the base

GitHub API URL, given earlier to `make-app-client`.  

The "path only" mode is useful when you are constructing the URL yourself and don't want to repeat the base API URL there.

The path can start with a `/` or not, which makes no difference, both cases are handled the same way.

The "full URL" mode is useful when you use a URL extracted from a webhook payload

and don't want to strip the base URL part from there.



```clj

;; Use github-api-url (provided earlier to make-app-client) as base API URL

(client/app-request @client :get "foo" {})

(client/app-request @client :get "/foo" {})

;; The same call, but without relying on github-api-url

(client/app-request @client :get "https://api.github.com/foo" {})

```



#### Convenience wrappers for API endpoints



This library does not provide any wrappers like



```clj

(list-issue-comments "owner" "repo" "123" {:since "2018-01-01"})

```



Such wrappers are really easy to implement on your own:



```clj

(defn create-list-issue-comments-request [owner repo issue-number params]

  {:method       :get

   :url          (format "/repos/%s/%s/issues/%s/comments" owner repo issue-number)

   :query-params params})

```



and then use like this:



```clj

(client/request @client 42 (create-list-issue-comments-request "owner" "repo" "123" {:since "2018-01-01"}))

```



Full GitHub API reference can be found [here](https://developer.github.com/v3/).



## Development



With every commit, add important changes from it to the "Unreleased" section of _CHANGELOG.md_.



### Release procedure



Run `lein release` as described below, depending on how much changes are made since previous release.



Library version will be updated in _project.clj_ and _README.md_ automatically after calling `lein release`.

`## Unreleased` section int _CHANGELOG.md_ will be automatically changed into the version being released.



    lein release :patch

    # or

    lein release :minor

    # or

    lein release :major



## License



Copyright © 2018 Dmitrii Balakhonskii



Distributed under the Eclipse Public License version 1.0.



[GitHub Apps]: https://developer.github.com/apps/about-apps/#about-github-apps

[Authenticating with GitHub Apps]: https://developer.github.com/apps/building-github-apps/authenticating-with-github-apps/

[webhook-signatures]: https://developer.github.com/webhooks/securing/#validating-payloads-from-github

[as-app]: https://developer.github.com/apps/building-github-apps/authenticating-with-github-apps/#accessing-api-endpoints-as-a-github-app

[as-installation]: https://developer.github.com/apps/building-github-apps/authenticating-with-github-apps/#accessing-api-endpoints-as-an-installation

[clj-http]: https://github.com/dakrone/clj-http

[mount-lite]: https://github.com/aroemers/mount-lite