Principle of Least Privilege: Why do fine-grained tokens require contents:write for workflow_dispatch?

[excalq]

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We have a configuration where a microservice's repo builds an image, then triggers a deployment via workflow_dispatch in our GitOps repo. As the default GITHUB_TOKEN can't be used to access other repos in our org (which would be a nice feature, given /settings/actions > Access implies this ability), we instead use a distinct Org-owned fine-grained Access Token, which we pass to peter-evans/repository-dispatch@v3.

The concern is that this token is required to have contents:write permissions. Read-only is not sufficient, nor is actions:write. This is a violation of the least-privilege security principle.

Without contents:write, the user encounters Error: Resource not accessible by personal access token.

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[21hs]

O problema que você está enfrentando ocorre devido às permissões específicas necessárias para o evento workflow_dispatch, que é usado para disparar workflows em um repositório diferente. Quando o evento workflow_dispatch é acionado via repository-dispatch (como no seu caso, com a ação peter-evans/repository-dispatch), o token de acesso granular precisa da permissão contents:write porque o GitHub trata esse evento como uma ação que pode envolver alterações no conteúdo do repositório. Embora disparar um workflow seja uma operação de leitura, o GitHub exige contents:write para garantir que a API consiga disparar o workflow e interagir com ele de forma completa.

Essa exigência pode parecer contra-intuitiva, já que disparar workflows geralmente não envolve modificar o conteúdo do repositório. No entanto, o GitHub usa contents:write como uma permissão mais ampla para invocar workflows via API, mesmo que o workflow em si não modifique diretamente o conteúdo. Isso garante que o token tenha permissões suficientes para lidar tanto com o disparo do workflow quanto com qualquer ação relacionada ao conteúdo dentro dos workflows.

Infelizmente, isso representa um trade-off entre segurança (o princípio de menor privilégio) e funcionalidade. O GitHub poderia refinar esse escopo de permissões, mas por enquanto, a permissão contents:write é necessária para disparar workflows via workflow_dispatch.

Se você está buscando uma abordagem mais restrita, pode ser necessário explorar alternativas, como usar escopos mais limitados dentro dos próprios workflows (por exemplo, restringir ações dentro do workflow disparado) para manter um equilíbrio entre segurança e funcionalidade.

[excalq]

Thank you @21hs for the detailed explanation.

In our use-case of a public repository triggering a deployment via a private repo workflow, this constraint means the public repository must have a token with full write-access to private repositories. This is a significant concern, as being public necessitates least-privilege access.

The private workflow repository has the purpose of keeping deployment infrastructure from being a concern in the public repo's workflows.

Considering the design of the API described above, why is the term "fine-grained" applicable? Given that "fine grained tokens" are in "beta", this type of feedback should be considered.