Security in a mobile app is mostly about reducing trust. The device can be inspected, network conditions can be hostile and client behavior can be modified. A secure integration assumes the backend remains the final authority.
Define the trust boundary
An iOS app should never be the only place where authorization, pricing, entitlement or transaction rules are enforced. The app can improve user experience with local validation, but the server must independently verify every sensitive operation.
Use standard transport security
Use HTTPS for every production endpoint and keep App Transport Security enabled. Avoid broad exceptions that silently allow insecure traffic.
Certificate pinning can reduce some interception risks, but it introduces operational complexity when certificates rotate. Use it only when the threat model justifies it and design a safe update strategy. It is not a replacement for authentication or server-side authorization.
Store sensitive tokens in Keychain
Authentication tokens do not belong in UserDefaults, source files or analytics properties. Use Keychain for credentials that must persist securely on the device.
protocol CredentialStore {
func save(_ token: AuthToken) throws
func readToken() throws -> AuthToken?
func clear() throws
}Wrap Keychain access behind a small interface so the rest of the app does not depend on security-framework details and tests can use an in-memory implementation.
Design token refresh as one coordinated flow
When several requests receive an expired-token response at the same time, they should not all refresh independently. Coordinate refresh behind an actor or another serialized component, then replay eligible requests after one successful refresh.
Set clear limits. If refresh fails because the session is no longer valid, clear credentials and move the user to authentication rather than entering an infinite retry loop.
Do not ship durable secrets in the app
Anything embedded in the application bundle can eventually be extracted. Do not rely on a static API secret in the client as proof that a request came from an untampered app.
For request signing, use short-lived credentials issued by a trusted backend or platform-supported attestation where appropriate. Long-lived private keys and provider secrets belong on the server.
Sanitize logs and errors
Logs are useful during debugging, but they can accidentally expose tokens, personal data, payment details or medical information. Build a logging policy that redacts sensitive headers and fields by default.
- Do not print full request or response bodies in production.
- Use correlation IDs instead of personal identifiers.
- Map backend errors to safe user-facing messages.
- Keep diagnostic detail in protected server logs.
Make sensitive requests resilient
Retries should be deliberate. A GET request may be safe to retry, while a payment or reservation action can create duplicates unless the API supports idempotency.
Use an idempotency key or stable operation identifier for actions that must execute once. Distinguish timeout from confirmed failure: when the network drops after submission, query the operation status before asking the user to try again.
Security checklist
- Sensitive decisions are enforced by the backend.
- All production traffic uses HTTPS without broad exceptions.
- Credentials are stored in Keychain and removed on logout.
- Token refresh is coordinated and bounded.
- No durable provider secret is embedded in the app.
- Logs redact tokens and personal data.
- Transactional requests support idempotency or status recovery.
