feat: Add Kubernetes authentication (#1778)

# What does this PR do?

This commit adds a new authentication system to the Llama Stack server
with support for Kubernetes and custom authentication providers. Key
changes include:

- Implemented KubernetesAuthProvider for validating Kubernetes service
account tokens
- Implemented CustomAuthProvider for validating tokens against external
endpoints - this is the same code that was already present.
- Added test for Kubernetes
- Updated server configuration to support authentication settings
- Added documentation for authentication configuration and usage

The authentication system supports:
- Bearer token validation
- Kubernetes service account token validation
- Custom authentication endpoints

## Test Plan

Setup a Kube cluster using Kind or Minikube.

Run a server with:

```
server:
  port: 8321
  auth:
    provider_type: kubernetes
    config:
      api_server_url: http://url
      ca_cert_path: path/to/cert (optional)
```

Run:

```
curl -s -L -H "Authorization: Bearer $(kubectl create token my-user)" http://127.0.0.1:8321/v1/providers
```

Or replace "my-user" with your service account.

Signed-off-by: Sébastien Han <seb@redhat.com>

.github/workflows/integration-auth-tests.yml

@@ -0,0 +1,136 @@
+name: Integration Auth Tests
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+    paths:
+      - 'distributions/**'
+      - 'llama_stack/**'
+      - 'tests/integration/**'
+      - 'uv.lock'
+      - 'pyproject.toml'
+      - 'requirements.txt'
+      - '.github/workflows/integration-auth-tests.yml' # This workflow
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  test-matrix:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        auth-provider: [kubernetes]
+      fail-fast: false # we want to run all tests regardless of failure
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@v5
+        with:
+          python-version: "3.10"
+
+      - name: Set Up Environment and Install Dependencies
+        run: |
+          uv sync --extra dev --extra test
+          uv pip install -e .
+          llama stack build --template ollama --image-type venv
+
+      - name: Install minikube
+        if: ${{ matrix.auth-provider == 'kubernetes' }}
+        uses: medyagh/setup-minikube@latest
+
+      - name: Start minikube
+        if: ${{ matrix.auth-provider == 'kubernetes' }}
+        run: |
+          minikube start
+          kubectl get pods -A
+
+      - name: Configure Kube Auth
+        if: ${{ matrix.auth-provider == 'kubernetes' }}
+        run: |
+          kubectl create namespace llama-stack
+          kubectl create serviceaccount llama-stack-auth -n llama-stack
+          kubectl create rolebinding llama-stack-auth-rolebinding --clusterrole=admin --serviceaccount=llama-stack:llama-stack-auth -n llama-stack
+          kubectl create token llama-stack-auth -n llama-stack > llama-stack-auth-token
+
+      - name: Set Kubernetes Config
+        if: ${{ matrix.auth-provider == 'kubernetes' }}
+        run: |
+          echo "KUBERNETES_API_SERVER_URL=$(kubectl config view --minify -o jsonpath='{.clusters[0].cluster.server}')" >> $GITHUB_ENV
+          echo "KUBERNETES_CA_CERT_PATH=$(kubectl config view --minify -o jsonpath='{.clusters[0].cluster.certificate-authority}')" >> $GITHUB_ENV
+
+      - name: Set Kube Auth Config and run server
+        env:
+          INFERENCE_MODEL: "meta-llama/Llama-3.2-3B-Instruct"
+        if: ${{ matrix.auth-provider == 'kubernetes' }}
+        run: |
+          run_dir=$(mktemp -d)
+          cat <<'EOF' > $run_dir/run.yaml
+          version: '2'
+          image_name: kube
+          apis:
+          - agents
+          - datasetio
+          - eval
+          - inference
+          - safety
+          - scoring
+          - telemetry
+          - tool_runtime
+          - vector_io
+          providers:
+            agents:
+            - provider_id: meta-reference
+              provider_type: inline::meta-reference
+              config:
+                persistence_store:
+                  type: sqlite
+                  namespace: null
+                  db_path: ${env.SQLITE_STORE_DIR:~/.llama/distributions/ollama}/agents_store.db
+            telemetry:
+            - provider_id: meta-reference
+              provider_type: inline::meta-reference
+              config:
+                service_name: "${env.OTEL_SERVICE_NAME:\u200B}"
+                sinks: ${env.TELEMETRY_SINKS:console,sqlite}
+                sqlite_db_path: ${env.SQLITE_DB_PATH:~/.llama/distributions/ollama/trace_store.db}
+          server:
+            port: 8321
+          EOF
+          yq eval '.server.auth = {"provider_type": "${{ matrix.auth-provider }}"}' -i $run_dir/run.yaml
+          yq eval '.server.auth.config = {"api_server_url": "${{ env.KUBERNETES_API_SERVER_URL }}", "ca_cert_path": "${{ env.KUBERNETES_CA_CERT_PATH }}"}' -i $run_dir/run.yaml
+          cat $run_dir/run.yaml
+
+          source .venv/bin/activate
+          nohup uv run llama stack run $run_dir/run.yaml --image-type venv > server.log 2>&1 &
+
+      - name: Wait for Llama Stack server to be ready
+        run: |
+          echo "Waiting for Llama Stack server..."
+          for i in {1..30}; do
+            if curl -s -L -H "Authorization: Bearer $(cat llama-stack-auth-token)" http://localhost:8321/v1/health | grep -q "OK"; then
+              echo "Llama Stack server is up!"
+              if grep -q "Enabling authentication with provider: ${{ matrix.auth-provider }}" server.log; then
+                echo "Llama Stack server is configured to use ${{ matrix.auth-provider }} auth"
+                exit 0
+              else
+                echo "Llama Stack server is not configured to use ${{ matrix.auth-provider }} auth"
+                cat server.log
+                exit 1
+              fi
+            fi
+            sleep 1
+          done
+          echo "Llama Stack server failed to start"
+          cat server.log
+          exit 1
+
+      - name: Test auth
+        run: |
+          curl -s -L -H "Authorization: Bearer $(cat llama-stack-auth-token)" http://127.0.0.1:8321/v1/providers|jq