rfc: add more details around token refreshing and caching

Signed-off-by: Sanskar Jaiswal <jaiswalsanskar078@gmail.com>

.github/workflows/action.yaml

@@ -0,0 +1,29 @@
+name: test-gh-action
+
+on:
+  pull_request:
+    paths:
+      - 'action/**'
+  push:
+    paths:
+      - 'action/**'
+    branches:
+      - 'main'
+      - 'release/**'
+
+permissions: read-all
+
+jobs:
+  actions:
+    strategy:
+      fail-fast: false
+      matrix:
+        version: [ubuntu-latest, macos-latest, windows-latest]
+
+    runs-on: ${{ matrix.version }}
+    name: action on ${{ matrix.version }}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@c85c95e3d7251135ab7dc9ce3241c5835cc595a9 # v3.5.3
+      - name: Setup flux
+        uses: ./action

.github/workflows/e2e-bootstrap.yaml

@@ -26,7 +26,7 @@ jobs:
             **/go.sum
             **/go.mod
       - name: Setup Kubernetes
-        uses: helm/kind-action@fa81e57adff234b2908110485695db0f181f3c67 # v1.7.0
+        uses: helm/kind-action@dda0770415bac9fc20092cacbc54aa298604d140 # v1.8.0
         with:
           version: v0.20.0
           cluster_name: kind

.github/workflows/e2e.yaml

@@ -30,7 +30,7 @@ jobs:
             **/go.sum
             **/go.mod
       - name: Setup Kubernetes
-        uses: helm/kind-action@fa81e57adff234b2908110485695db0f181f3c67 # v1.7.0
+        uses: helm/kind-action@dda0770415bac9fc20092cacbc54aa298604d140 # v1.8.0
         with:
           version: v0.20.0
           cluster_name: kind

.github/workflows/release.yaml

@@ -32,7 +32,7 @@ jobs:
         uses: docker/setup-qemu-action@2b82ce82d56a2a04d2637cd93a637ae1b359c0a7 # v2.2.0
       - name: Setup Docker Buildx
         id: buildx
-        uses: docker/setup-buildx-action@16c0bc4a6e6ada2cfd8afd41d22d95379cf7c32a  # v2.8.0
+        uses: docker/setup-buildx-action@4c0219f9ac95b02789c1075625400b2acbff50b1  # v2.9.1
       - name: Setup Syft
         uses: anchore/sbom-action/download-syft@78fc58e266e87a38d4194b2137a3d4e9bcaf7ca1 # v0.14.3
       - name: Setup Cosign

action/README.md

@@ -1,216 +1,22 @@
 # Flux GitHub Action
 
-Usage:
+To install the latest Flux CLI on Linux, macOS or Windows GitHub runners:
 
 ```yaml
-    steps:
+steps:
-      - name: Setup Flux CLI
+  - name: Setup Flux CLI
-        uses: fluxcd/flux2/action@main
+    uses: fluxcd/flux2/action@main
-      - name: Run Flux commands
+    with:
-        run: flux -v
+      version: 'latest'
+  - name: Run Flux CLI
+    run: flux version --client
 ```
 
-The latest stable version of the `flux` binary is downloaded from
+The Flux GitHub Action can be used to automate various tasks in CI, such as:
-GitHub [releases](https://github.com/fluxcd/flux2/releases)
-and placed at `/usr/local/bin/flux`.
 
-Note that this action can only be used on GitHub **Linux** runners.
+- [Automate Flux upgrades on clusters via Pull Requests](https://fluxcd.io/flux/flux-gh-action/#automate-flux-updates)
-You can change the arch (defaults to `amd64`) with:
+- [Push Kubernetes manifests to container registries](https://fluxcd.io/flux/flux-gh-action/#push-kubernetes-manifests-to-container-registries)
+- [Run end-to-end testing with Flux and Kubernetes Kind](https://fluxcd.io/flux/flux-gh-action/#end-to-end-testing)
 
-```yaml
+For more information, please see the [Flux GitHub Action documentation](/flux/flux-gh-action.md).
-    steps:
-      - name: Setup Flux CLI
-        uses: fluxcd/flux2/action@main
-        with:
-          arch: arm64 # can be amd64, arm64 or arm
-```
 
-You can download a specific version with:
-
-```yaml
-    steps:
-      - name: Setup Flux CLI
-        uses: fluxcd/flux2/action@main
-        with:
-          version: 0.32.0
-```
-
-You can also authenticate against the GitHub API using GitHub Actions' `GITHUB_TOKEN` secret.
-
-For more information, please [read about the GitHub token secret](https://docs.github.com/en/actions/security-guides/automatic-token-authentication#about-the-github_token-secret).
-
-```yaml
-    steps:
-      - name: Setup Flux CLI
-        uses: fluxcd/flux2/action@main
-        with:
-          token: ${{ secrets.GITHUB_TOKEN }}
-```
-
-This is useful if you are seeing failures on shared runners, those failures are usually API limits being hit.
-
-### Automate Flux updates
-
-Example workflow for updating Flux's components generated with `flux bootstrap --path=clusters/production`:
-
-```yaml
-name: update-flux
-
-on:
-  workflow_dispatch:
-  schedule:
-    - cron: "0 * * * *"
-
-permissions:
-  contents: write
-  pull-requests: write
-
-jobs:
-  components:
-    runs-on: ubuntu-latest
-    steps:
-      - name: Check out code
-        uses: actions/checkout@v3
-      - name: Setup Flux CLI
-        uses: fluxcd/flux2/action@main
-      - name: Check for updates
-        id: update
-        run: |
-          flux install \
-            --export > ./clusters/production/flux-system/gotk-components.yaml
-
-          VERSION="$(flux -v)"
-          echo "flux_version=$VERSION" >> $GITHUB_OUTPUT
-      - name: Create Pull Request
-        uses: peter-evans/create-pull-request@v4
-        with:
-            token: ${{ secrets.GITHUB_TOKEN }}
-            branch: update-flux
-            commit-message: Update to ${{ steps.update.outputs.flux_version }}
-            title: Update to ${{ steps.update.outputs.flux_version }}
-            body: |
-              ${{ steps.update.outputs.flux_version }}
-```
-
-### Push Kubernetes manifests to container registries
-
-Example workflow for publishing Kubernetes manifests bundled as OCI artifacts to GitHub Container Registry:
-
-```yaml
-name: push-artifact-staging
-
-on:
-  push:
-    branches:
-      - 'main'
-
-permissions:
-  packages: write # needed for ghcr.io access
-
-env:
-  OCI_REPO: "oci://ghcr.io/my-org/manifests/${{ github.event.repository.name }}"
-
-jobs:
-  kubernetes:
-    runs-on: ubuntu-latest
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v3
-      - name: Setup Flux CLI
-        uses: fluxcd/flux2/action@main
-      - name: Login to GHCR
-        uses: docker/login-action@v2
-        with:
-          registry: ghcr.io
-          username: ${{ github.actor }}
-          password: ${{ secrets.GITHUB_TOKEN }}
-      - name: Generate manifests
-        run: |
-          kustomize build ./manifests/staging > ./deploy/app.yaml
-      - name: Push manifests
-        run: |
-          flux push artifact $OCI_REPO:$(git rev-parse --short HEAD) \
-            --path="./deploy" \
-            --source="$(git config --get remote.origin.url)" \
-            --revision="$(git branch --show-current)@sha1:$(git rev-parse HEAD)"
-      - name: Deploy manifests to staging
-        run: |
-          flux tag artifact $OCI_REPO:$(git rev-parse --short HEAD) --tag staging
-```
-
-### Push and sign Kubernetes manifests to container registries
-
-Example workflow for publishing Kubernetes manifests bundled as OCI artifacts
-which are signed with Cosign and GitHub OIDC:
-
-```yaml
-name: push-sign-artifact
-
-on:
-  push:
-    branches:
-      - 'main'
-
-permissions:
-  packages: write # needed for ghcr.io access
-  id-token: write # needed for keyless signing
-
-env:
-  OCI_REPO: "oci://ghcr.io/my-org/manifests/${{ github.event.repository.name }}"
-
-jobs:
-  kubernetes:
-    runs-on: ubuntu-latest
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v3
-      - name: Setup Flux CLI
-        uses: fluxcd/flux2/action@main
-      - name: Setup Cosign
-        uses: sigstore/cosign-installer@main
-      - name: Login to GHCR
-        uses: docker/login-action@v2
-        with:
-          registry: ghcr.io
-          username: ${{ github.actor }}
-          password: ${{ secrets.GITHUB_TOKEN }}
-      - name: Push and sign manifests
-        run: |
-          digest_url=$(flux push artifact \
-          $OCI_REPO:$(git rev-parse --short HEAD) \
-          --path="./manifests" \
-          --source="$(git config --get remote.origin.url)" \
-          --revision="$(git branch --show-current)@sha1:$(git rev-parse HEAD)" |\
-          jq -r '. | .repository + "@" + .digest')
-
-          cosign sign $digest_url
-```
-
-### End-to-end testing
-
-Example workflow for running Flux in Kubernetes Kind:
-
-```yaml
-name: e2e
-
-on:
-  push:
-    branches:
-      - '*'
-
-jobs:
-  kubernetes:
-    runs-on: ubuntu-latest
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v3
-      - name: Setup Flux CLI
-        uses: fluxcd/flux2/action@main
-      - name: Setup Kubernetes Kind
-        uses: engineerd/setup-kind@v0.5.0
-      - name: Install Flux in Kubernetes Kind
-        run: flux install
-```
-
-A complete e2e testing workflow is available here
-[flux2-kustomize-helm-example](https://github.com/fluxcd/flux2-kustomize-helm-example/blob/main/.github/workflows/e2e.yaml)

action/action.yml

@@ -1,64 +1,120 @@
 name: Setup Flux CLI
-description: A GitHub Action for running Flux commands
+description: A GitHub Action for installing the Flux CLI
-author: Stefan Prodan
+author: Flux project
 branding:
   color: blue
   icon: command
 inputs:
   version:
-    description: "Flux version e.g. 0.8.0 (defaults to latest stable release)"
+    description: "Flux version e.g. 2.0.0 (defaults to latest stable release)"
     required: false
   arch:
     description: "arch can be amd64, arm64 or arm"
-    required: true
+    required: false
-    default: "amd64"
+    deprecationMessage: "No longer required, action will now detect runner arch."
   bindir:
-    description: "Optional location of the Flux binary. Will not use sudo if set. Updates System Path."
+    description: "Alternative location for the Flux binary, defaults to path relative to $RUNNER_TOOL_CACHE."
     required: false
   token:
-    description: "GitHub Token used to authentication against the API (generally only needed to prevent quota limit errors)"
+    description: "Token used to authentication against the GitHub.com API. Defaults to the token from the GitHub context of the workflow."
     required: false
 runs:
   using: composite
   steps:
-    - name: "Download flux binary to tmp"
+    - name: "Download the binary to the runner's cache dir"
       shell: bash
       run: |
-        ARCH=${{ inputs.arch }}
         VERSION=${{ inputs.version }}
-        TOKEN=${{ inputs.token }}
 
-        if [ -z "${VERSION}" ]; then
+        TOKEN=${{ inputs.token }}
-          if [ -n "${TOKEN}" ]; then
+        if [[ -z "$TOKEN" ]]; then
-            VERSION_SLUG=$(curl https://api.github.com/repos/fluxcd/flux2/releases/latest --silent --location --header "Authorization: token ${TOKEN}" | grep tag_name)
+          TOKEN=${{ github.token }}
-          else
+        fi
-            # With no GITHUB_TOKEN you will experience occasional failures due to rate limiting
+
-            # Ref: https://github.com/fluxcd/flux2/issues/3509#issuecomment-1400820992
+        if [[ -z "$VERSION" ]] || [[ "$VERSION" = "latest" ]]; then
-            VERSION_SLUG=$(curl https://api.github.com/repos/fluxcd/flux2/releases/latest --silent --location | grep tag_name)
+          VERSION=$(curl -fsSL -H "Authorization: token ${TOKEN}" https://api.github.com/repos/fluxcd/flux2/releases/latest | grep tag_name | cut -d '"' -f 4)
+        fi
+        if [[ -z "$VERSION" ]]; then
+          echo "Unable to determine Flux CLI version"
+          exit 1
+        fi
+        if [[ $VERSION = v* ]]; then
+          VERSION="${VERSION:1}"
+        fi
+
+        OS=$(echo "${RUNNER_OS}" | tr '[:upper:]' '[:lower:]')
+        if [[ "$OS" == "macos" ]]; then
+          OS="darwin"
+        fi
+
+        ARCH=$(echo "${RUNNER_ARCH}" | tr '[:upper:]' '[:lower:]')
+        if [[ "$ARCH" == "x64" ]]; then
+          ARCH="amd64"
+        elif [[ "$ARCH" == "x86" ]]; then
+          ARCH="386"
+        fi
+
+        FLUX_EXEC_FILE="flux"
+        if [[ "$OS" == "windows" ]]; then
+            FLUX_EXEC_FILE="${FLUX_EXEC_FILE}.exe"
+        fi
+
+        FLUX_TOOL_DIR=${{ inputs.bindir }}
+        if [[ -z "$FLUX_TOOL_DIR" ]]; then
+          FLUX_TOOL_DIR="${RUNNER_TOOL_CACHE}/flux2/${VERSION}/${OS}/${ARCH}"
+        fi
+        if [[ ! -x "$FLUX_TOOL_DIR/FLUX_EXEC_FILE" ]]; then
+          DL_DIR="$(mktemp -dt flux2-XXXXXX)"
+          trap 'rm -rf $DL_DIR' EXIT
+
+          echo "Downloading flux ${VERSION} for ${OS}/${ARCH}"
+          FLUX_TARGET_FILE="flux_${VERSION}_${OS}_${ARCH}.tar.gz"
+          if [[ "$OS" == "windows" ]]; then
+            FLUX_TARGET_FILE="flux_${VERSION}_${OS}_${ARCH}.zip"
           fi
 
-          VERSION=$(echo "${VERSION_SLUG}" | sed -E 's/.*"([^"]+)".*/\1/' | cut -c 2-)
+          FLUX_CHECKSUMS_FILE="flux_${VERSION}_checksums.txt"
+
+          FLUX_DOWNLOAD_URL="https://github.com/fluxcd/flux2/releases/download/v${VERSION}/"
+
+          curl -fsSL -o "$DL_DIR/$FLUX_TARGET_FILE" "$FLUX_DOWNLOAD_URL/$FLUX_TARGET_FILE"
+          curl -fsSL -o "$DL_DIR/$FLUX_CHECKSUMS_FILE" "$FLUX_DOWNLOAD_URL/$FLUX_CHECKSUMS_FILE"
+
+          echo "Verifying checksum"
+          sum=""
+          if command -v openssl > /dev/null; then
+            sum=$(openssl sha256 "$DL_DIR/$FLUX_TARGET_FILE" | awk '{print $2}')
+          elif command -v sha256sum > /dev/null; then
+            sum=$(sha256sum "$DL_DIR/$FLUX_TARGET_FILE" | awk '{print $1}')
+          fi
+
+          if [[ -z "$sum" ]]; then
+            echo "Neither openssl nor sha256sum found. Cannot calculate checksum."
+            exit 1
+          fi
+
+          expected_sum=$(grep " $FLUX_TARGET_FILE\$" "$DL_DIR/$FLUX_CHECKSUMS_FILE" | awk '{print $1}')
+          if [ "$sum" != "$expected_sum" ]; then
+            echo "SHA sum of ${FLUX_TARGET_FILE} does not match. Aborting."
+            exit 1
+          fi
+
+          echo "Installing flux to ${FLUX_TOOL_DIR}"
+          mkdir -p "$FLUX_TOOL_DIR"
+        
+          if [[ "$OS" == "windows" ]]; then
+            unzip "$DL_DIR/$FLUX_TARGET_FILE" "$FLUX_EXEC_FILE" -d "$FLUX_TOOL_DIR"
+          else
+            tar xzf "$DL_DIR/$FLUX_TARGET_FILE" -C "$FLUX_TOOL_DIR" $FLUX_EXEC_FILE
+          fi
+
+          chmod +x "$FLUX_TOOL_DIR/$FLUX_EXEC_FILE"
         fi
 
-        BIN_URL="https://github.com/fluxcd/flux2/releases/download/v${VERSION}/flux_${VERSION}_linux_${ARCH}.tar.gz"
+        echo "Adding flux to path"
-        curl --silent --fail --location "${BIN_URL}" --output /tmp/flux.tar.gz
+        echo "$FLUX_TOOL_DIR" >> "$GITHUB_PATH"
-        mkdir -p /tmp/flux
+
-        tar -C /tmp/flux/ -zxvf /tmp/flux.tar.gz
+    - name: "Print installed flux version"
-    - name: "Copy Flux binary to execute location"
-      shell: bash
-      run: |
-        BINDIR=${{ inputs.bindir }}
-        if [ -z "${BINDIR}" ]; then
-          sudo cp /tmp/flux/flux /usr/local/bin
-        else
-          cp /tmp/flux/flux "${BINDIR}"
-          echo "${BINDIR}" >> $GITHUB_PATH
-        fi
-    - name: "Cleanup tmp"
-      shell: bash
-      run: |
-        rm -rf /tmp/flux/ /tmp/flux.tar.gz
-    - name: "Verify correct installation of binary"
       shell: bash
       run: |
         flux -v

rfcs/0006-git-repo-passwordless-auth/README.md

@@ -0,0 +1,209 @@
+# RFC-0006 Passwordless authentication for Git repositories
+
+**Status:** provisional
+
+**Creation date:** 2023-31-07
+
+## Summary
+
+Flux should provide a mechanism to authenticate against Git repositories without
+the use of passwords. This RFC proposes the use of alternative authentication
+methods like OIDC, OAuth2 and IAM to access Git repositories hosted on specific
+Git SaaS platforms and cloud providers.
+
+## Motivation
+
+At the moment, Flux supports HTTP basic and bearer authentication. Users are
+required to create a Secret containing the username and the password/bearer
+token, which is then referred to in the GitRepository using `.spec.secretRef`.
+
+While this works fine, it has a couple of drawbacks:
+* Scalability: Each new GitRepository potentially warrants another credentials
+pair, which doesn't scale well in big organizations with hundreds of
+repositories with different owners, increasing the risk of mismanagement and
+leaks.
+* Identity: A username is associated with an actual human. But often, the
+repository belongs to a team of 2 or more people. This leads to a problem where
+teams have to decide whose credentials should Flux use for authentication.
+
+These problems exist not due to flaws in Flux, but because of the inherent
+nature of password based authentication.
+
+With support for OIDC, OAuth2 and IAM based authentication, we can eliminate
+these problems:
+* Scalability: Since OIDC is fully handled by the cloud provider, it eliminates
+any user involvement in managing credentials. For OAuth2 and IAM, users do need
+to provide certain information like the ID of the resource, private key, etc.
+but these are still a better alternative to passwords since the same resource
+can be reused by multiple teams with different members.
+* Identity: Since all the above authentication methods are associated with a
+virtual resource independent of a user, it solves the problem of a single person
+being tied to automation that several people are involved in.
+
+### Goals
+
+* Integrate with major cloud providers' OIDC and IAM offerings to provide a
+seamless way of Git repository authentication.
+* Integrate with major Git SaaS providers to support their app based OAuth2
+mechanism.
+
+### Non-Goals
+* Replace the existing basic and bearer authentication API.
+
+## Proposal
+
+A new string field `.spec.provider` shall be added to the GitRepository API.
+The field will be an enum with the following variants:
+* `azure`
+* `github`
+* `gcp`
+
+> AWS CodeCommit is not supported as it does not support authentication via IAM
+Roles without the use of https://github.com/aws/git-remote-codecommit.
+
+By default, it will be blank, which indicates that the user wants to
+authenticate via HTTP basic/bearer auth or SSH.
+
+### Azure
+
+Git repositories hosted on Azure Devops can be accessed by Flux using OIDC if
+the cluster running Flux is hosted on AKS with [managed identity](https://learn.microsoft.com/en-us/azure/devops/integrate/get-started/authentication/service-principal-managed-identity?view=azure-devops)
+enabled. The managed identity associated with the cluster must have sufficient
+permissions to be able to access Azure Devops resources. This enables Flux to
+access the Git repository without the need for any credentials.
+
+```yaml
+apiVersion: source.toolkit.fluxcd.io/v1
+kind: GitRepository
+metadata:
+  name: azure-devops
+spec:
+  interval: 1m
+  url: https://dev.azure.com/<org>/<project>/_git/<repository>
+  ref:
+    branch: master
+  # notice the lack of secretRef
+  provider: azure
+```
+
+### GCP
+
+Git repositories hosted on Google Cloud Source Repositories can be accessed by
+Flux via a [GCP Service Account](https://cloud.google.com/iam/docs/service-account-overview).
+The Service Account must have sufficient permissions to be able to access Google
+Cloud Source Repositories and its credentials should be specified in the secret
+referred to in `.spec.secretRef`.
+
+```yaml
+apiVersion: source.toolkit.fluxcd.io/v1
+kind: GitRepository
+metadata:
+  name: gcp-repo
+spec:
+  interval: 1m
+  url: https://source.developers.google.com/p/<project>/r/<repository>
+  ref:
+    branch: master
+  provider: gcp
+  secretRef:
+    name: gcp-sa
+---
+kind: Secret
+metadata:
+  name: gcp-sa
+stringData:
+  gcpServiceAccount: |
+    {
+      "type": "service_account",
+      "project_id": "my-google-project",
+      "private_key_id": "REDACTED",
+      "private_key": "-----BEGIN PRIVATE KEY-----\nREDACTED\n-----END PRIVATE KEY-----\n",
+      "client_email": "<service-account-id>@my-google-project.iam.gserviceaccount.com",
+      "client_id": "REDACTED",
+      "auth_uri": "https://accounts.google.com/o/oauth2/auth",
+      "token_uri": "https://oauth2.googleapis.com/token",
+      "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
+      "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/<service-account-id>%40my-google-project.iam.gserviceaccount.com"
+    }
+```
+
+### GitHub
+
+Git repositories hosted on GitHub can be accessed via [GitHub Apps](https://docs.github.com/en/apps/overview).
+This allows users to create a single resource from which they can access all
+their GitHub repositories. The app must have sufficient permissions to be able
+to access repositories. The app's ID, private key and installation ID should
+be mentioned in the Secret referred to by `.spec.secretRef`. GitHub Enterprise
+users will also need to mention their GitHub API URL in the Secret.
+
+```yaml
+apiVersion: source.toolkit.fluxcd.io/v1
+kind: GitRepository
+metadata:
+  name: github-repo
+spec:
+  interval: 1m
+  url: https://github.com/<org>/<repository>
+  ref:
+    branch: master
+  provider: github
+  secretRef:
+    name: github-app
+---
+kind: Secret
+metadata:
+  name: gcp-sa
+stringData:
+  githubAppID: <app-id>
+  githubInstallationID: <installation-id>
+  githubPrivateKey: |
+    <PEM-private-key>
+  githubApiURl: <github-enterprise-api-url> #optional, required only for GitHub Enterprise users
+```
+
+## Design Details
+
+### Azure
+
+If `.spec.provider` is set to `azure`, Flux controllers will reach out to
+[Azure IMDS (Instance Metadata Service)](https://learn.microsoft.com/en-us/azure/active-directory/managed-identities-azure-resources/how-to-use-vm-token#get-a-token-using-go)
+to get an access token. This [access token will be then used as a bearer token](https://learn.microsoft.com/en-us/azure/devops/integrate/get-started/authentication/service-principal-managed-identity?view=azure-devops#q-can-i-use-a-service-principal-to-do-git-operations-like-clone-a-repo)
+to perform HTTP bearer authentication.
+
+### GCP
+
+If `.spec.provider` is set to `gcp`, Flux controllers will get the Service
+Account credentials from the specified Secret and use
+[`google.CredentialsFromJSON`](https://pkg.go.dev/golang.org/x/oauth2/google#CredentialsFromJSON)
+to fetch the access token. This access token will be then used as the password
+and the `client_email` as the username to perform HTTP basic authentication.
+
+### GitHub
+
+If `.spec.provider` is set to `github`, Flux controllers will get the app
+details from the specified Secret and use it to [generate an app installation
+token](https://docs.github.com/en/apps/creating-github-apps/authenticating-with-a-github-app/generating-an-installation-access-token-for-a-github-app).
+This token is then used as the password and [`x-access-token` as the username](https://docs.github.com/en/apps/creating-github-apps/registering-a-github-app/choosing-permissions-for-a-github-app#choosing-permissions-for-git-access)
+to perform HTTP basic authentication.
+
+### Token Caching and Refreshing
+
+To avoid calling the upstream API for a token during every reconciliation, Flux
+controllers shall cache the token after fetching it. Since GitHub tokens
+self-expire, the cache shall automatically evict the token after it has expired,
+triggering a fetch of a fresh token.
+For GCP, the [`TokenSource`](https://pkg.go.dev/golang.org/x/oauth2@v0.10.0#TokenSource)
+object will be cached, since it automatically handles refreshing an expired
+token and always returns a valid token. Since a `TokenSource` never expires, it
+need not be evicted from the cache.
+While Azure's managed identities subsystem caches the token, it is
+[recommended for the consumer application to implement their own caching](https://learn.microsoft.com/en-us/azure/active-directory/managed-identities-azure-resources/how-to-use-vm-token#token-caching)
+as well.
+The caches for all three providers are separate, i.e. there shall exist a
+dedicated cache for each provider.
+
+Since the proposed authentication methods for GitHub and GCP involve some form
+of credentials stored in a Kubernetes Secret, the cache key can be the Secret's
+`<namespace/name>`. Since authentication for Azure is configured directly via
+the source-controller Deployment, the token can just be stored in a global
+variable, which is refreshed whenever the token expires.