Let users submit their own OpenAI or Anthropic API keys to an authenticated server endpoint over TLS, keep the keys out of browser and mobile code, and decrypt them only on the backend component that needs to call the provider. If the application must remember a key, store it encrypted and keep the encryption key in a separate, restricted key-management boundary. If it does not need to remember one, discard it after the operation and tell users they will need to enter it again.
Why a server-side design matters
A provider key is a secret credential, not ordinary user preference data. OpenAI explicitly warns developers not to expose keys in client-side code such as browsers or apps, and recommends loading them from a server environment variable or key-management service. OpenAI API Reference: Authentication
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Anthropic likewise advises against putting API keys directly in code or configuration files and describes using secret-management facilities when passing keys to cloud applications. Anthropic API key best practices
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Choose whether to retain a user’s key
Do not retain it when you do not need to
If a feature can complete the provider operation immediately, keep the submitted value only for that request and discard it afterward. Explain the trade-off in the interface: the user will have to enter the key again next time. This minimizes retained secret data; it is an architectural choice, not a provider requirement.
Encrypt it when the product must remember it
For persistent BYOK support, encrypt the key before saving it. Store ciphertext and necessary non-secret metadata in the application database; do not store the encryption key alongside that ciphertext. OWASP recommends keeping encryption keys separate from encrypted data where possible. A managed secrets or key-management service can provide that separation, subject to its access model and operational requirements. OWASP Cryptographic Storage Cheat Sheet
Encryption at rest is only one layer. Limit which backend components and operators can decrypt secrets, authorize every use against the account that owns the key, redact secret-bearing data from logs and diagnostics, and provide a way to replace or remove credentials. OWASP’s secrets guidance discusses secret-management practices and the additional protection, complexity, and administrative overhead that dedicated systems can entail. OWASP Secrets Management Cheat Sheet
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Implement the intake and provider-call flow
- Authenticate first. Require a valid user session or equivalent authorization before accepting a key. Bind the credential record to an internal account identifier, not an identifier supplied by the client.
- Accept the key over TLS. Send it in a server request body to your application, not in a URL or client-side code. OpenAI’s authentication guidance says: “Do not share it with others or expose it in any client-side code (browsers, apps).” OpenAI API Reference: Authentication
- Validate only if useful. If the product needs to check a credential, make a minimal provider request from the backend. Do not log the submitted value or echo it in an error response. The exact validation operation depends on the provider API and is not specified by the cited key-handling guidance.
- Persist safely, if required. Prefer a managed secrets facility when its access controls and operational model fit. Otherwise, encrypt the key before writing it to the database and keep the key-encryption key in a separately restricted key-management service. Store ciphertext and non-secret metadata only.
- Authorize and decrypt at use time. For each provider call, check that the requesting user may use the stored credential. Decrypt it only in the backend component that needs it, then send it to the chosen provider over TLS.
- Keep secrets out of observability data. Redact credentials from traces, exception messages, metrics labels, request dumps, support logs, and debugging output. Treat provider error bodies as potentially sensitive rather than assuming they are safe to retain.
- Support lifecycle actions. Let users replace or remove saved keys. Record lifecycle events without recording the secret. Verify provider-specific revocation and rotation procedures in current official documentation before presenting exact instructions.
Compare secret-management approaches by operational fit
| Decision area | Application-managed encryption | Managed secrets or key-management service |
|---|---|---|
| Decryption access | Your application design must restrict which components can access the encryption key and decrypt stored credentials. | Evaluate the service’s access controls and how your application is authorized to retrieve or use secrets. |
| Key retention | Can support persistent storage, but requires you to implement encryption and access controls. | Can centralize secret handling; whether the application can avoid retaining user keys depends on the service and integration. |
| Rotation and revocation | You must define the application’s credential replacement and deletion workflow. | Assess how the service supports your workflow, alongside provider-side key rotation or revocation. |
| Audit and redaction | You must design auditing while ensuring secret values are not recorded. | Assess available audit controls, and still redact secrets from application logs and diagnostics. |
| Operational burden | Requires secure implementation and ongoing maintenance of encryption and access controls. | May add protection and simplify management, but OWASP notes dedicated systems can add complexity and administrative overhead. |
Provider-specific detail: Anthropic expiration choices
Anthropic’s Claude Platform authentication documentation describes preset expiration periods for Console-created keys of 3 hours, 1 day, 7 days, or 30 days, a custom duration, or “Never” when the key is stored in a secrets manager and rotated by the customer. These are Anthropic-specific choices documented on its current platform page; check that page for the latest details before relying on them. Claude Platform Authentication
The OpenAI source cited here establishes safe server-side handling, but does not establish matching key-expiration options. Do not assume Anthropic’s expiration choices apply to OpenAI.
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