GitHub App authentication (#1830)

* add config options for github_app_*

* add github app auth

* add/adapt integration tests for github app auth

* fix scope of fixture

* pass env vars in tox

* add unit test to ensure coverage

* change tests to run additionally for github app auth

* add reason to skipif

* skip some tests for github app auth

* fix if condition

* bump minor version

* update docs

* Kick off CI build

* try out github app on cbartz-org/cbartz-repo-policy-compliance-tests

* update README on test repository requirements

* skip non-applicable tests

* Revert "try out github app on cbartz-org/cbartz-repo-policy-compliance-tests"

This reverts commit 5a9ce51.

* cleanup

* update docs

* use AuthMode enum and remove asserts

* try out github app on cbartz-org/cbartz-repo-policy-compliance-tests

* Revert "try out github app on cbartz-org/cbartz-repo-policy-compliance-tests"

This reverts commit 6db8f17.

.github/workflows/tests.yaml

@@ -18,7 +18,10 @@ jobs:
       - name: Run tests (unit + integration)
         id: run-tests
         env:
-          GITHUB_TOKEN: ${{ secrets.PERSONAL_GITHUB_TOKEN }}
+          AUTH_GITHUB_TOKEN: ${{ secrets.PERSONAL_GITHUB_TOKEN }}
+          AUTH_GITHUB_APP_ID : ${{ secrets.TEST_GITHUB_APP_ID }}
+          AUTH_GITHUB_APP_INSTALLATION_ID : ${{ secrets.TEST_GITHUB_APP_INSTALLATION_ID }}
+          AUTH_GITHUB_APP_PRIVATE_KEY : ${{ secrets.TEST_GITHUB_APP_PRIVATE_KEY }}
         run: |
           # Ensure that stdout appears as normal and redirect to file and exit depends on exit code of first command
           STDOUT_LOG=$(mktemp --suffix=stdout.log)

README.md

@@ -46,15 +46,21 @@ failing check to be used for testing purposes.
 There are two types of test: the application test and the charm test.
 
 ### Application tests
-To run the application tests, the `GITHUB_TOKEN` environment variable must be set. This
+To run the application tests, the `AUTH_GITHUB_TOKEN` environment variable must be set. This
 should be a token of a user with full repo permissions for the test repository. 
+You can also pass in `AUTH_APP_ID`, `AUTH_INSTALLATION_ID`, and `AUTH_PRIVATE_KEY` 
+to test the authentication using GitHub App Auth. In that case, the tests will additionally
+be executed using GitHub app auth. Note that the GitHub app should be installed
+in the test repository organisation/user namespace, with access granted to the test repository.
+
 The command `tox -e test` can be used to run all tests, which are primarily integration tests.
 You can also select the repository against which to run the tests by setting
 the `--repository` flag. The tests will fork the repository and create PRs against it.
 Note that the tests are currently designed to work for specific Canonical repositories, 
-and may need to be for other repositories 
+and may need to be adapted for other repositories 
 (e.g. `tests.app.integration.test_target_branch_protection.test_fail` 
-assumes that certain collaborators are in the `users_bypass_pull_request_allowances` list).
+assumes that certain collaborators are in the `users_bypass_pull_request_allowances` list). 
+The test repository must also have a branch protection defined for the main branch.
 Also note that the forks are created in the personal space of the user whose token is being used, 
 and that the forks are not deleted after the run. 
 The reason for this is that it is only possible to create one fork of a repository, 
@@ -66,6 +72,8 @@ bot to test things like comments from a user with no write permissions or above.
 GitHub actions should have access to the GitHub token via a secret
 called `PERSONAL_GITHUB_TOKEN`. It is recommended to use either a fine-grained PAT or a 
 token that is short-lived, e.g. 7 days. When it expires, a new token must be set.
+For the GitHub App Auth, the `TEST_GITHUB_APP_ID`, `TEST_GIHUB_APP_INSTALLATION_ID`, and
+`TEST_GITHUB_APP_PRIVATE_KEY` should be set as secrets.
 
 ### Charm tests
 

charm/charmcraft.yaml

@@ -48,9 +48,35 @@ config:
         write and higher permissions for the repository to run jobs from forks.
       type: boolean
       default: false
+    github_app_id:
+      description: >-
+        The app or client ID of the GitHub App to use for communication with GitHub.
+        If provided, the other github_app_* options must also be provided.
+        The Github App needs to have read permission for Administration. If private repositories
+        are checked, the Github App does also need read permission for Contents and Pull request.
+        Either this or the github_token must be provided.
+      type: string
+    github_app_installation_id:
+      description: >-
+        The installation ID of the GitHub App to use for communication with GitHub.
+        If provided, the other github_app_* options must also be provided.
+        The Github App needs to have read permission for Administration. If private repositories
+        are checked, the Github App does also need read permission for Contents and Pull request.
+        Either this or the github_token must be provided.
+      type: string
+    github_app_private_key:
+      # this will become a juju user secret once paas-app-charmer supports it
+      description: >-
+        The private key of the GitHub App to use for communication with GitHub.
+        If provided, the other github_app_* options must also be provided.
+        The Github App needs to have read permission for Administration. If private repositories
+        are checked, the Github App does also need read permission for Contents and Pull request.
+        Either this or the github_token must be provided.
+      type: string
     github_token:
       description: >-
         The token to use for communication with GitHub. This can be a PAT (with repo scope)
         or a fine-grained token with read permission for Administration. If private repositories 
         are checked, the fine-grained token does also need read permission for Contents and 
         Pull request.
+        Either this or the GitHub App configuration must be provided.

charm/docs/reference/github-auth.md

@@ -0,0 +1,30 @@
+# GitHub Authentication
+
+This section describes the GitHub authentication options available for the charm.
+
+You can either choose to use
+
+- classic personal access tokens
+- fine-grained personal access tokens
+- a GitHub app
+
+for authentication. The latter two options are recommended for better security and access control.
+They require the fine-grained permissions as mentioned below.
+
+**Note**:  If you are using a personal access tokens rather than a GitHub app,
+the user who owns the token must have administrative access to the organisation or repository,
+in addition to having a token with the necessary permissions.
+
+
+## Classic personal access token scopes
+
+If you want to use classic personal access tokens, you will need to select the `repo` 
+scope when generating them.
+
+## Fine grained permissions
+
+For fine-grained access control, the following repository permissions are required:
+
+- Administration: read
+- Contents: read (if you want to check private repositories)
+- Pull requests: read (if you want to check private repositories)

pyproject.toml

@@ -3,7 +3,7 @@
 
 [tool.poetry]
 name = "repo-policy-compliance"
-version = "1.9.2"
+version = "1.10.0"
 description = "Checks GitHub repository settings for compliance with policy"
 authors = ["Canonical IS DevOps <launchpad.net/~canonical-is-devops>"]
 license = "Apache 2.0"

repo_policy_compliance/github_client.py

@@ -2,15 +2,16 @@
 # See LICENSE file for licensing details.
 
 """Module for GitHub client."""
-
+import enum
 import functools
 import logging
 import os
+from enum import Enum
 from typing import Callable, Concatenate, Literal, ParamSpec, TypeVar, cast
 from urllib import parse
 
 from github import BadCredentialsException, Github, GithubException, RateLimitExceededException
-from github.Auth import Token
+from github.Auth import AppAuth, AppInstallationAuth, Auth, Token
 from github.Branch import Branch
 from github.Repository import Repository
 from urllib3 import Retry
@@ -27,23 +28,49 @@
 
 # Bandit thinks this constant is the real Github token
 GITHUB_TOKEN_ENV_NAME = "GITHUB_TOKEN"  # nosec
+GITHUB_APP_ID_ENV_NAME = "GITHUB_APP_ID"
+GITHUB_APP_INSTALLATION_ID_ENV_NAME = "GITHUB_APP_INSTALLATION_ID"
+GITHUB_APP_PRIVATE_KEY_ENV_NAME = "GITHUB_APP_PRIVATE_KEY"
+
+MISSING_GITHUB_CONFIG_ERR_MSG = (
+    f"Either the {GITHUB_TOKEN_ENV_NAME} or not all of {GITHUB_APP_ID_ENV_NAME},"
+    f" {GITHUB_APP_INSTALLATION_ID_ENV_NAME}, {GITHUB_APP_PRIVATE_KEY_ENV_NAME} "
+    f"environment variables were provided or are empty, "
+    "the variables are needed for interactions with GitHub, "
+)
+NOT_ALL_GITHUB_APP_CONFIG_ERR_MSG = (
+    f"Not all of {GITHUB_APP_ID_ENV_NAME}, {GITHUB_APP_INSTALLATION_ID_ENV_NAME},"
+    f" {GITHUB_APP_PRIVATE_KEY_ENV_NAME} environment variables were provided, "
+)
+# the following is no hardcoded password
+PROVIDED_GITHUB_TOKEN_AND_APP_CONFIG_ERR_MSG = (  # nosec
+    "Provided github app config and github token, only one of them should be provided, "
+)
+
+
+class _AuthMode(Enum):
+    """Enum to represent the auth mode to use.
+
+    Attributes:
+        TOKEN: Using GitHub token auth.
+        APP: Using GitHub App auth.
+    """
+
+    TOKEN = enum.auto()
+    APP = enum.auto()
 
 
 def get() -> Github:
     """Get a GitHub client.
 
     Returns:
-        A GitHub client that is configured with a token from the environment.
+        A GitHub client that is configured with a token or GitHub app from the environment.
 
     Raises:
-        ConfigurationError: If the GitHub token environment variable is not provided or empty.
-    """
-    github_token = os.getenv(GITHUB_TOKEN_ENV_NAME) or os.getenv(f"FLASK_{GITHUB_TOKEN_ENV_NAME}")
-    if not github_token:
-        raise ConfigurationError(
-            f"The {GITHUB_TOKEN_ENV_NAME} environment variable was not provided or empty, "
-            f"it is needed for interactions with GitHub, got: {github_token!r}"
-        )
+        ConfigurationError: If the GitHub auth config is not valid.
+    """  # noqa: DCO051 error raised is useful to know for the user of the public interface
+    auth = _get_auth()
+
     # Only retry on 5xx and only retry once after 20 secs
     retry_config = Retry(
         total=1,
@@ -53,7 +80,123 @@ def get() -> Github:
         raise_on_status=False,
         raise_on_redirect=False,
     )
-    return Github(auth=Token(github_token), retry=retry_config)
+    return Github(auth=auth, retry=retry_config)
+
+
+def _get_auth() -> Auth:
+    """Get a GitHub auth object.
+
+    Returns:
+        A GitHub auth object that is configured with a token from the environment.
+    """
+    github_token = os.getenv(GITHUB_TOKEN_ENV_NAME) or os.getenv(f"FLASK_{GITHUB_TOKEN_ENV_NAME}")
+    github_app_id = os.getenv(GITHUB_APP_ID_ENV_NAME) or os.getenv(
+        f"FLASK_{GITHUB_APP_ID_ENV_NAME}"
+    )
+    github_app_installation_id_str = os.getenv(GITHUB_APP_INSTALLATION_ID_ENV_NAME) or os.getenv(
+        f"FLASK_{GITHUB_APP_INSTALLATION_ID_ENV_NAME}"
+    )
+    github_app_private_key = os.getenv(GITHUB_APP_PRIVATE_KEY_ENV_NAME) or os.getenv(
+        f"FLASK_{GITHUB_APP_PRIVATE_KEY_ENV_NAME}"
+    )
+
+    auth_mode = _get_auth_mode(
+        github_token=github_token,
+        github_app_id=github_app_id,
+        github_app_installation_id_str=github_app_installation_id_str,
+        github_app_private_key=github_app_private_key,
+    )
+
+    auth: Auth
+    if auth_mode == _AuthMode.APP:
+        auth = _get_github_app_installation_auth(
+            github_app_id=cast(str, github_app_id),
+            github_app_installation_id_str=cast(str, github_app_installation_id_str),
+            github_app_private_key=cast(str, github_app_private_key),
+        )
+    else:
+        assert github_token is not None  # nosec
+        auth = Token(github_token)
+
+    return auth
+
+
+def _get_auth_mode(
+    github_token: str | None,
+    github_app_id: str | None,
+    github_app_installation_id_str: str | None,
+    github_app_private_key: str | None,
+) -> _AuthMode:
+    """Get the auth mode to use.
+
+    Args:
+        github_token: The GitHub token.
+        github_app_id: The GitHub App ID or Client ID.
+        github_app_installation_id_str: The GitHub App Installation ID as a string.
+        github_app_private_key: The GitHub App private key.
+
+    Raises:
+        ConfigurationError: If the configuration is not valid, e.g. if both a token and app config
+            are provided.
+
+    Returns:
+        The auth mode to use.
+    """
+    if not github_token and not (
+        github_app_id or github_app_installation_id_str or github_app_private_key
+    ):
+        raise ConfigurationError(
+            f"{MISSING_GITHUB_CONFIG_ERR_MSG}"
+            f"got: {github_token!r}, {github_app_id!r},"
+            f" {github_app_installation_id_str!r}, {github_app_private_key!r}"
+        )
+    if github_token and (
+        github_app_id or github_app_installation_id_str or github_app_private_key
+    ):
+        raise ConfigurationError(
+            f"{PROVIDED_GITHUB_TOKEN_AND_APP_CONFIG_ERR_MSG}"
+            f"got: {github_token!r}, {github_app_id!r}, {github_app_installation_id_str!r},"
+            f" {github_app_private_key!r}"
+        )
+
+    if github_app_id or github_app_installation_id_str or github_app_private_key:
+        if not (github_app_id and github_app_installation_id_str and github_app_private_key):
+            raise ConfigurationError(
+                f"{NOT_ALL_GITHUB_APP_CONFIG_ERR_MSG}"
+                f"got: {github_app_id!r}, {github_app_installation_id_str!r}, "
+                f"{github_app_private_key!r}"
+            )
+
+    if github_token:
+        return _AuthMode.TOKEN
+    return _AuthMode.APP
+
+
+def _get_github_app_installation_auth(
+    github_app_id: str, github_app_installation_id_str: str, github_app_private_key: str
+) -> AppInstallationAuth:
+    """Get a GitHub App Installation Auth object.
+
+    Args:
+        github_app_id: The GitHub App ID or Client ID.
+        github_app_installation_id_str: The GitHub App Installation ID as a string.
+        github_app_private_key: The GitHub App private key.
+
+    Returns:
+        A GitHub App Installation Auth object.
+
+    Raises:
+        ConfigurationError: If the GitHub App Installation Auth config is not valid.
+    """
+    try:
+        github_app_installation_id = int(github_app_installation_id_str)
+    except ValueError as exc:
+        raise ConfigurationError(
+            f"Invalid github app installation id {github_app_installation_id_str!r}, "
+            f"it should be an integer."
+        ) from exc
+    app_auth = AppAuth(app_id=github_app_id, private_key=github_app_private_key)
+    return AppInstallationAuth(app_auth=app_auth, installation_id=github_app_installation_id)
 
 
 def inject(func: Callable[Concatenate[Github, P], R]) -> Callable[P, R]:

rockcraft.yaml

@@ -3,7 +3,7 @@
 
 name: repo-policy-compliance
 base: [email protected]
-version: '1.9.2'
+version: '1.10.0'
 summary: Check the repository setup for policy compliance
 description: |
     Used to check whether a GitHub repository complies with expected policies.