Today I'm gonna tell you everything about the GITHUB_TOKEN in GitHub Actions. You will learn what it is, how it works, how to customize its behavior, and how to limit or change its permissions.
Video
As usual, if you are a visual learner, or simply prefer to watch and listen instead of reading, here you have the video with the whole explanation and demo, which to be fair is much more complete than this post.
Link to the video: https://youtu.be/jEK07KPEjnY
If you rather prefer reading, well... let's just continue :)
What is GITHUB_TOKEN
Let's start with what the GITHUB_TOKEN is in GitHub Actions and how it works.
The GITHUB_TOKEN is a special access token that you can use to authenticate on behalf of GitHub Actions. GitHub automatically creates a GITHUB_TOKEN secret for you to use in your workflow, and you can use it to authenticate in a workflow run.
The way this works is that when you enable GitHub Actions in a repository, GitHub installs a GitHub App on that. The GITHUB_TOKEN secret is basically a GitHub App installation access token.
Before each job begins, GitHub fetches an installation access token for the job from that GitHub App. Since the App has access to a single repo, the token's permissions are limited to the repository that contains your workflow. And to make it even more secure, the token expires when the job is finished.
Hope the mechanism is now clearer. Let's quickly see how to use a GITHUB_TOKEN
Use GitHub Token
There are 2 ways to use the token: from secrets and from the context.
- uses: actions/labeler@v2
with:
repo-token: ${{ secrets.GITHUB_TOKEN }}
In this first example we use the secrets.GITHUB_TOKEN to consume it. As mentioned, the secret is automatically generated so you can just use it straight away.
- name: Create a Release
id: create_release
uses: actions/create-release@v1
env:
GITHUB_TOKEN: ${{ github.token }}
Here instead we use the GitHub context, which contains the token. Note that the two are equivalent.
Personal Access Token vs GITHUB_TOKEN
If you are thinking _"why should I use the GITHUB_TOKEN instead of my normal PAT?", remember that a Personal Access Token is always available, so if someone is able to steal that PAT they can potentially do some harm.
The GITHUB_TOKEN instead expires just right after the job is over. So even if someone is able to steal it (which is almost impossible), they basically can't do anything wrong.
Default Permissions
By Default, the GITHUB_TOKEN has a quite comprehensive list of permissions assigned to it.
This table shows the permissions granted to the GITHUB_TOKEN by default. Good thing is that people with admin permissions to an enterprise, organization, or repository can set the default permissions to be either permissive or restricted.
The Permissions UI
So, let's see how we can change the permissions of the GITHUB_TOKEN to make it even more secure.
Just go to your repository or organization Settings, then click on Actions.
In here you can change the permissions assigned to your token by choosing Read and Write (which allows you to access the content and make changes) or Read-only.
That is super quick to do, but on the other hand pretty limited. What if I want to assign permissions in a more granular way?
Granular permissions via YAML
You can use the permissions key in the YAML workflow file to modify permissions for the GITHUB_TOKEN for an entire workflow or for individual jobs.
permissions:
contents: write
pull-requests: write
issues: read
packages: none
And you can use all the permissions that are listed in the table above. Additionally, as you can see below, it supports intellisense if you do it in the GitHub interface directly:
When the permissions key is used, all unspecified permissions are set to no access, with the exception of the metadata scope, which always gets read access.
You can personalize the token permissions either at Job level, or at whole workflow level (or actually both):
[...]
permissions:
contents: write
pull-requests: write
jobs:
job1:
runs-on: ubuntu-latest
steps:
[...]
job2:
runs-on: ubuntu-latest
permissions:
issues: write
steps:
[...]
Conclusions
Hope you have now a better understanding about the GITHUB_TOKEN, what it does and how we can set its permissions properly. Let me know in the comment section below if you have any other questions about it.
Also, check out this video where I talk about creating Personal Access Tokens in GitHub.
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Top comments (3)
I am using Githubactions with codebuild but each time the CodeBuild stage starts to run,I am getting Error message: The Security token included in the request is invalid.please can you help with how to fix it?
Run aws-actions/aws-codebuild-run-build@v1
with:
project-name: CodeBuild
buildspec-override: dev-env/buildspec.yml
env-vars-for-codebuild: TF_INPUT,
AWS_ACCESS_KEY_ID,
AWS_SECRET_ACCESS_KEY,
AWS_REGION,
ROLE_TO_ASSUME,
ROLE_DURATION_SECONDS,
env:
tf_version: latest
tg_version: latest
AWS_DEFAULT_REGION: us-east-2
AWS_REGION: us-east-1
AWS_ACCESS_KEY_ID: ***
AWS_SECRET_ACCESS_KEY: ***
AWS_SESSION_TOKEN: ***
TF_INPUT: false
ROLE_TO_ASSUME: ***
ROLE_DURATION_SECONDS: 3600
**STARTING CODEBUILD**
Error: The security token included in the request is invalid
**CODEBUILD COMPLETE**
It means there is something wrong with your credentials. Either the accessKeyId or secretAccessKey (or both) are wrong. You can try validating your credentials using the AWS cli using the STS get caller identity call before using them in your code.
Great explanation! Determining the correct token permissions can be a challenge, and automated solutions can be quite helpful. app.stepsecurity.io calculates minimum GITHUB_TOKEN permissions automatically and also applies other GitHub Actions Security best practices. I'm sharing this in case others find it useful too!