Reservations and Authorization in OCPP

By Michael Samuel Naeem · November 5, 2025 · 7 min read

A driver reserves a charger for 6 PM, arrives at 6:05, and finds another vehicle charging on "their" connector. The reservation expired at 6:00 because the CSMS set a 30-minute window and the driver's meeting ran long. Reservations and authorization are the access control layer of OCPP—who can charge, on which connector, and for how long. Get authorization wrong and you bill the wrong account. Get reservations wrong and drivers stop trusting your network.

Authorization flow

User presents ID tag (RFID, app, credit card)
  → Charger sends Authorize(idTag) to CSMS
  → CSMS responds: Accepted / Blocked / Expired / Invalid
  → If Accepted: StartTransaction
  → If not: reject, display reason

Authorize request/response:

// Request
{ "idTag": "RFID-0042-A" }

// Response
{
  "idTagInfo": {
    "status": "Accepted",
    "expiryDate": "2026-06-01T00:00:00Z",
    "parentIdTag": "FLEET-ACME-CORP"
  }
}

Local authorization list

For offline operation and reduced latency, cache authorized tags:

{
  "listVersion": 15,
  "localAuthorizationList": [
    {
      "idTagInfo": {
        "status": "Accepted",
        "expiryDate": "2026-01-01T00:00:00Z",
        "parentIdTag": "FLEET-ACME"
      },
      "idTag": "RFID-0042-A"
    }
  ]
}

CSMS updates via SendLocalList:

{
  "listVersion": 16,
  "updateType": "Differential",
  "localAuthorizationList": [
    { "idTag": "RFID-0099-B", "idTagInfo": { "status": "Accepted" } }
  ]
}

Differential adds/updates entries. Full replaces the entire list. Increment listVersion on every update.

Reservations

CSMS reserves a connector:

{
  "connectorId": 2,
  "expiryDate": "2025-11-05T18:30:00Z",
  "idTag": "RFID-0042-A",
  "reservationId": 101
}

Charger response:

{ "status": "Accepted" }
// or: "Faulted", "Occupied", "Rejected", "Unavailable"

While reserved:

• Connector status shows Reserved.
• Only the matching ID tag can start a transaction.
• Other tags are rejected even if otherwise authorized.
• Reservation auto-cancels at expiryDate.

Cancel reservation:

{ "reservationId": 101 }

Parent ID tag billing

def process_authorization(id_tag: str, auth_response: dict) -> BillingAccount:
    parent = auth_response.get("parentIdTag")
    billing_tag = parent if parent else id_tag

    account = db.get_account(billing_tag)
    if not account:
        raise BillingError(f"No account for {billing_tag}")

    if account.balance <= 0 and account.payment_method == "prepaid":
        return reject("Insufficient balance")

    return account

Fleet scenario: 50 drivers, each with RFID-XXXX child tags under FLEET-ACME parent. All sessions bill to the fleet account.

Concurrent transaction handling

Prevent one user from occupying multiple connectors:

def check_concurrent(id_tag: str, csms) -> bool:
    active = csms.get_active_transactions(id_tag)
    if active:
        return False  # ConcurrentTx
    return True

Configure per account: fleet accounts may allow 2 concurrent sessions; individual users get 1.

Authorization cache on charger

OCPP 1.6 supports LocalAuthListEnabled and AuthorizationCacheEnabled:

Authorize(idTag) → check cache (TTL: LocalAuthorizeOfflineParam)
                 → check local list
                 → send to CSMS (if online)
                 → cache response

Cache TTL of 300 seconds reduces CSMS load. Clear cache entry when CSMS sends ClearCache.

Reservation UX considerations

• Expiry buffer: Set reservation 15 minutes past the user's requested time.
• Grace period: Allow 5 minutes after expiry before releasing to others.
• Notification: Push notification 10 minutes before expiry via the mobile app (outside OCPP).
• No-show tracking: After 3 no-shows, require immediate arrival or shorten reservation windows.

OCPP 2.0.1 authorization improvements

OCPP 2.0.1 replaces flat authorization with structured IdToken types:

{
  "idToken": {
    "idToken": "RFID-ABC123",
    "type": "ISO14443"
  },
  "certificate": "base64-ocsp-response"
}

Supported IdToken types: Central, eMAID (ISO 15118 Plug & Charge), ISO14443, ISO15693, KeyCode, Local, NoAuthorization. Each type has different validation rules — eMAID requires certificate chain validation against V2G root CA.

Plug & Charge (ISO 15118) authorization flow:

EV presents eMAID → charger validates certificate → CSMS Authorize(eMAID)
→ contract certificate verified → charging starts without RFID tap

Offline authorization fallback

When CSMS is unreachable, chargers must decide locally:

Authorize(idTag):
  1. Check local auth list (pre-synced whitelist)
  2. Check authorization cache (recent successful auths)
  3. If AllowOfflineTxForUnknownIdEnabled → accept unknown tags
  4. Else → reject with Blocked status

Configure LocalAuthListMaxLength and sync frequency based on expected offline duration. Fleet depots with reliable connectivity can use shorter cache TTL; highway stations need longer offline tolerance.

Reservation conflict resolution

Multiple reservation scenarios need explicit handling:

Log all reservation state transitions — disputes about no-shows require audit trail.

Failure modes

• Cache stale after account suspension — revoked user charges offline
• Concurrent session not checked — double billing on same idTag
• Reservation expiry not enforced locally — connector blocked after user no-show
• Plug & Charge cert expired — authorization fails silently; need OCSP check
• Local auth list not synced — new subscribers can't charge offline

Production checklist

• Authorization cache TTL configured per deployment type
• Local auth list synced on subscription change
• Concurrent session check before Authorize response
• Reservation grace period and no-show policy documented
• Plug & Charge certificate validation with OCSP
• Offline authorization policy explicit (allow vs deny unknown tags)

Authorization edge cases from the field

• Stale cache after card theft report — force ClearCache on affected sites when EMSP sends block list updates.
• Reservation ID collision after CSMS restore — reservation IDs must be globally unique per station; restore from backup can reuse IDs; increment from max on recovery.
• MAC address auth on free chargers — NoAuthorization mode still needs abuse rate limits per connector.

OCPI token alignment for roaming

Roaming drivers present EMSP tokens that your local auth list may not include. Flow:

RFID tap → lookup local list (miss) → OCPI real-time authorize → cache Accepted for TTL
         → OCPP Authorize → StartTransaction

Cache roaming authorizations with short TTL (5–15 minutes) — EMSP can revoke contracts mid-session rarely, but blocked accounts should propagate within minutes. Log authorization_source: local | ocpi | csms on each session for settlement disputes.

GroupId and fleet policies

OCPP 2.0.1 IdTokenInfo may include groupIdToken for fleet grouping. Use it for concurrent session limits:

def max_concurrent_sessions(id_token_info):
    group = id_token_info.get("groupIdToken")
    if group and group.id_token.startswith("FLEET-"):
        return 4  # fleet policy
    return 1

Parent ID tags and group tokens interact — document precedence in your auth module so billing and concurrency rules do not contradict.

Contract certificate validation latency

Plug & Charge OCSP checks add 200–800ms to authorization. Cache OCSP responses per contract certificate with TTL under nextUpdate. Timeout path: reject with user-visible "try RFID" rather than silent fail — drivers blame charger, not PKI.

Authorization analytics

Dashboard: Invalid rate by site, ConcurrentTx by fleet account, reservation no-show rate by app channel. Spikes in Invalid after marketing campaign often mean stale local list, not fraud.

QR and app-initiated reservation

Mobile app reservations use same reservationId as RFID — CSMS must bind reservation to idTag or idToken consistently. Deep link opens app → confirms reservation → charger shows Reserved before driver arrives.

Waitlist when reserved connector occupied

When reserved connector still occupied at expiry, offer alternate connector via app push if available — OCPP ReserveNow on backup connector requires CSMS orchestration. Log user acceptance rate for waitlist offers.

Reservation deposit integration

Paid reservations tie ReserveNow to payment capture — cancel before window refunds deposit via CSMS billing module linked to reservationId.

Resources

• OCPP 1.6 Authorization — Authorize and Local Auth List
• OCPP 1.6 Reservations — ReserveNow and CancelReservation
• OCPP 2.0.1 Authorization — updated auth flows
• ISO 14443 RFID standard — contactless card protocol
• OCPI tokens module — cross-network authorization