feat: adding support for a proxy

README.md

@@ -4,9 +4,7 @@
 
 ## Limitations
 
-Due to how GitHub handles permissions in PRs coming from forks, this action is limited to PRs based on branches. See this issue: https://github.community/t/github-actions-are-severely-limited-on-prs/18179/4 for more detail.
-
-I'm currently investigating a workaround via a simple bot you can easily deploy. More soon...
+Due to how GitHub handles permissions in PRs coming from forks you will need to deploy an app if you want to post comments in those situations. [See below](#proxy-for-fork-based-prs).
 
 ## Usage
 
@@ -60,6 +58,31 @@ jobs:
 | allow-repeats         | with     | A boolean flag to allow identical messages to be posted each time this action is run                                        | no       | false   |
 | GITHUB_TOKEN          | env      | A valid GitHub token, can alternatively be defined in the env                                                               | maybe    |         |
 
+## Proxy for Fork-based PRs
+
+GitHub limits `GITHUB_TOKEN` and other API access token permissions when creating a PR from a fork. This makes it impossible to add comments when your PRs are coming from forks, which is the norm for open source projects. To work around this situation I've created a simple companion app you can deploy to Cloud Run or another environment to proxy the create comment requests and escalate the token privileges.
+
+See this issue: https://github.community/t/github-actions-are-severely-limited-on-prs/18179/4 for more detail.
+
+**Example**
+
+```yaml
+on:
+  pull_request:
+
+jobs:
+  pr:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: mshick/add-pr-comment@v1
+        with:
+          message: |
+            **Howdie!**
+          proxy-url: https://add-pr-comment-proxy-94idvmwyie-uc.a.run.app/
+          proxy-secret: foobar
+          repo-token: ${{ secrets.GITHUB_TOKEN }}
+```
+
 ## Features
 
 - Fast, runs in the GitHub Actions node.js runtime; no Docker pull needed.

action.yml

@@ -14,6 +14,12 @@ inputs:
     description: "Allow messages to be repeated."
     required: false
     default: "false"
+  proxy-url:
+    description: "Proxy URL for comment creation"
+    required: false
+  proxy-secret:
+    description: "A secret to use for authenticating against the proxy"
+    required: false
 branding:
   icon: message-circle
   color: purple

add-pr-comment.ts

@@ -4,13 +4,7 @@ import {HttpClient} from '@actions/http-client'
 import {Endpoints, RequestHeaders, IssuesListCommentsResponseData} from '@octokit/types'
 
 type ListCommitPullsResponse = Endpoints['GET /repos/:owner/:repo/commits/:commit_sha/pulls']['response']['data']
-
-interface AddPrCommentInputs {
-  allowRepeats: boolean
-  message: string
-  repoToken?: string
-  repoTokenUserLogin?: string
-}
+type CreateIssueCommentResponseData = Endpoints['POST /repos/:owner/:repo/issues/:issue_number/comments']['response']['data']
 
 interface ListCommitPullsParams {
   repoToken: string
@@ -40,6 +34,35 @@ const listCommitPulls = async (params: ListCommitPullsParams): Promise<ListCommi
 const getIssueNumberFromCommitPullsList = (commitPullsList: ListCommitPullsResponse): number | null =>
   commitPullsList.length ? commitPullsList[0].number : null
 
+interface CreateCommentProxyParams {
+  repoToken: string
+  body: string
+  owner: string
+  repo: string
+  issueNumber: number
+  proxyUrl: string
+  proxySecret: string
+}
+
+const createCommentProxy = async (params: CreateCommentProxyParams): Promise<CreateIssueCommentResponseData | null> => {
+  const {repoToken, owner, repo, issueNumber, body, proxyUrl, proxySecret} = params
+
+  const http = new HttpClient('http-client-add-pr-comment')
+
+  const additionalHeaders: RequestHeaders = {
+    authorization: `basic ${Buffer.from(proxySecret + ':').toString('base64')}`,
+    ['temporary-github-token']: repoToken,
+  }
+
+  const response = await http.postJson<CreateIssueCommentResponseData>(
+    `${proxyUrl}/repos/${owner}/${repo}/issues/${issueNumber}/comments`,
+    {body},
+    additionalHeaders,
+  )
+
+  return response.result
+}
+
 const isMessagePresent = (
   message: AddPrCommentInputs['message'],
   comments: IssuesListCommentsResponseData,
@@ -58,10 +81,21 @@ const isMessagePresent = (
   })
 }
 
+interface AddPrCommentInputs {
+  allowRepeats: boolean
+  message: string
+  proxySecret?: string
+  proxyUrl?: string
+  repoToken?: string
+  repoTokenUserLogin?: string
+}
+
 const getInputs = (): AddPrCommentInputs => {
   return {
     allowRepeats: Boolean(core.getInput('allow-repeats') === 'true'),
     message: core.getInput('message'),
+    proxySecret: core.getInput('proxy-secret'),
+    proxyUrl: core.getInput('proxy-url'),
     repoToken: core.getInput('repo-token') || process.env['GITHUB_TOKEN'],
     repoTokenUserLogin: core.getInput('repo-token-user-login'),
   }
@@ -69,7 +103,7 @@ const getInputs = (): AddPrCommentInputs => {
 
 const run = async (): Promise<void> => {
   try {
-    const {allowRepeats, message, repoToken, repoTokenUserLogin} = getInputs()
+    const {allowRepeats, message, repoToken, repoTokenUserLogin, proxyUrl, proxySecret} = getInputs()
 
     if (!repoToken) {
       throw new Error('no github token provided, set one with the repo-token input or GITHUB_TOKEN env variable')
@@ -125,12 +159,28 @@ const run = async (): Promise<void> => {
     }
 
     if (shouldCreateComment) {
+      if (proxyUrl) {
+        if (!proxySecret) {
+          throw new Error('proxy-url defined, but proxy-secret is missing')
+        }
+
+        await createCommentProxy({
+          owner,
+          repo,
+          issueNumber,
+          body: message,
+          repoToken,
+          proxyUrl,
+          proxySecret,
+        })
+      } else {
         await octokit.issues.createComment({
           owner,
           repo,
           issue_number: issueNumber,
           body: message,
         })
+      }
 
       core.setOutput('comment-created', 'true')
     } else {