[BUG] Vault-action does not support authentication only usage

[Ameausoone]

Describe the bug
I want to use vault-action only to authenticate to vault instance with an approle, and generate a VAULT_TOKEN to use with Terraform and vault-provider, and without retrieve secrets. But vault-action require to specify secrets.

To Reproduce
Use vault-action without secrets :

      - name: Authenticate to Vault
        uses: hashicorp/vault-action@v2.1.0
        with:
          url: https://my-vault-instance
          method: approle
          roleId: ${{ secrets.VAULT_ROLE_ID }}
          secretId: ${{ secrets.VAULT_SECRET_ID }}
          exportToken: true

Expected behavior

vault-action should authenticate and produces a masked environment variable VAULT_TOKEN.

Log Output

Error: Input required and not supplied: secrets

Additional context
N/A

[jasonodonnell]

@Ameausoone One way to trick this would be to do a look-up self: https://www.vaultproject.io/api-docs/auth/token#lookup-a-token-self.

We should definitely have support for exporting tokens only, though!

[ps-jay]

Is this a duplicate of #289, which is now solved by #299 (and released in https://github.com/hashicorp/vault-action/releases/tag/v2.4.1) ?

[tvoran]

Yep, looks like this was solved in #299. Thanks!