docs: update auth section with actual Authentik flow

- Document client_credentials flow for service accounts
- Add JWT claims structure (permissions, memory_*)
- Document available service accounts
- Add capabilities table with group mappings

API.md

@@ -573,7 +573,7 @@ curl -X GET https://api.riotpiao.com/ \
 
 ### Bearer Token (JWT)
 
-All operations except `/healthz` and `/readyz` require authentication.
+All operations except `/healthz` and `/readyz` require authentication via Authentik-issued JWT.
 
 ```bash
 curl -H 'Authorization: Bearer <jwt-token>' \
@@ -582,31 +582,76 @@ curl -H 'Authorization: Bearer <jwt-token>' \
 
 ### Obtaining Tokens
 
-**Via Authentik OIDC (human login):**
+**Service Account (client_credentials flow):**
+
+For programmatic access (agents, CI, scripts), use a service account:
+
 ```bash
-core auth login --username [email protected]
+# Get credentials from k8s secret (once)
+CLIENT_ID=$(kubectl -n portfolio get secret portfolio-agent-oidc -o jsonpath='{.data.CLIENT_ID}' | base64 -d)
+CLIENT_SECRET=$(kubectl -n portfolio get secret portfolio-agent-oidc -o jsonpath='{.data.CLIENT_SECRET}' | base64 -d)
+
+# Exchange for access token
+TOKEN=$(curl -s -X POST https://authentik.riotpiao.com/application/o/token/ \
+  -d "grant_type=client_credentials" \
+  -d "client_id=$CLIENT_ID" \
+  -d "client_secret=$CLIENT_SECRET" \
+  -d "scope=openid profile groups permissions memory" | jq -r '.access_token')
+
+# Use token
+curl -H "Authorization: Bearer $TOKEN" \
+  https://api.riotpiao.com/v1/models
 ```
 
-**Via service account (programmatic):**
+**Available service accounts:**
-```bash
+- `portfolio-agent` — Portfolio app (memory:read on homelab/portfolio projects)
-core mwinit login --username service-account --password secret
+- `memory-agent` — Memory service internal (memory:* on all projects)
-export RIOTPIAO_TOKEN=$(cat ~/.talos/.riotpiao-auth)
 
-curl -H "Authorization: Bearer $RIOTPIAO_TOKEN" \
+**Human login (authorization_code flow):**
-  https://api.riotpiao.com/v1/models
+
+Browser-based OAuth2 via Authentik. Used by web apps, not CLI.
+
+```
+1. Redirect to: https://authentik.riotpiao.com/application/o/authorize/
+   ?client_id=<app>&response_type=code&redirect_uri=<callback>&scope=openid+profile+groups+permissions
+2. User authenticates
+3. Exchange code for token at /application/o/token/
+```
+
+### JWT Claims
+
+Authentik tokens include these custom claims:
+
+```json
+{
+  "sub": "hashed-user-id",
+  "groups": ["homelab-admins", "llm-admins"],
+  "permissions": ["llm:inference", "llm:read", "llm:write"],
+  "memory_projects": ["homelab", "portfolio"],
+  "memory_visibility": "public",
+  "memory_role": "user"
+}
 ```
 
 ### Capabilities (RBAC)
 
-Tokens embed capabilities in claims. Required capabilities:
+The `permissions` claim contains capabilities. Gateway checks these:
 
-- `llm:inference` — `/v1/*` chat/embeddings/rerank
+| Capability | Required for | Granted to |
-- `workflow:execute` — `/workflow` operations
+|------------|--------------|------------|
-- `memory:read` — Memory queries
+| `llm:inference` | `/v1/chat/completions`, `/v1/embeddings`, `/v1/rerank` | llm-admins, llm-users |
-- `memory:write` — Memory ingest
+| `memory:read` | Memory queries | memory-users, memory-writers, poimen-memory-admins |
-- `sqs:access` — Queue operations
+| `memory:write` | Memory ingest | memory-writers, poimen-memory-admins |
-- `s3:access` — S3 operations
+| `memory:admin` | Memory admin ops | poimen-memory-admins |
-- `iam:admin` — IAM management
+| `*` | Everything | homelab-admins |
+
+**Memory-specific claims:**
+
+| Claim | Description |
+|-------|-------------|
+| `memory_projects` | Projects user can access (`["*"]` = all) |
+| `memory_visibility` | Max visibility level (`public`, `private`) |
+| `memory_role` | Role for memory service (`user`, `admin`, `portfolio-agent`) |
 
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