The Tool Desk
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How to choose between OAuth and an API key
Start with what the API must know and enforce. If it must know which user or workload authorized an action, or apply user-specific permissions, use delegated OAuth or another identity system that provides those controls. If the integration needs only a server-side application or project credential and the provider documents suitable restrictions, a dedicated API key may be sufficient.
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Google Cloud describes its own distinction this way: “API keys are for projects, authentication is for users.” That is a useful summary of Google’s standard API keys, which do not identify a principal; it is not a universal definition of every provider’s API key. Check the target API’s documentation to establish what a key identifies, what it authorizes, and how it can be disabled. Google Cloud: Why and when to use API keys
OAuth and API keys compared
| Question | OAuth token or delegation | API key |
|---|---|---|
| What identity can it represent? | A user or workload principal, through the authorization system. | Often an application or project. Google’s standard API keys do not identify a principal; other providers may differ. |
| How is authority constrained? | Scopes, resource restrictions, and action limits can narrow access; the resource server must validate and enforce them. | Provider-dependent. Restrictions may limit APIs, clients, or environments without establishing end-user authorization. |
| How does delegation work? | Token exchange can obtain a token for delegated or impersonated access, subject to the deployment’s policy. | Usually carries the key’s configured authority. User delegation requires another mechanism if the provider supports it. |
| How is access withdrawn? | An authorization server may revoke tokens or refresh-token grants. Short-lived access tokens can limit the useful life of a stolen token, but revocation behavior depends on the system. | Disable, delete, or regenerate it as the provider specifies. A key without an expiration may remain usable until that action. |
| What operational work is required? | Authorization-server or workload-identity setup, consent where relevant, token handling, and correct validation. | Secure storage, restrictions, isolation, monitoring, and a rotation plan. |
| Best fit | User delegation, granular authorization, distinct audit identity, and centrally managed access. | Server-side project identification, quota attribution, or an API specifically designed for key-based access. |
This is a design comparison, not a guarantee that every OAuth deployment is safer than every API-key scheme. Provider-specific behavior and the agent’s runtime exposure matter. IETF RFC 9700: Best Current Practice for OAuth 2.0 Security
#1 Best Overall
- POWERFUL SECURITY KEY: The Security Key C NFC is the essential physical passkey for protecting your digital life from phishing attacks. It ensures only you can access your accounts.
- WORKS WITH 1000+ ACCOUNTS: Compatible with Google, Microsoft, and Apple. A single Security Key C NFC secures 100 of your favorite accounts, including email, password managers, and more.
- FAST & CONVENIENT LOGIN: Plug in your Security Key C NFC via USB-C and tap it, or tap it against your phone (NFC) to authenticate. No batteries, no internet connection, and no extra fees required.
- TRUSTED PASSKEY TECHNOLOGY: Uses the latest passkey standards (FIDO2/WebAuthn & FIDO U2F) but does not support One-Time Passwords. For complex needs, check out the YubiKey 5 Series.
- BUILT TO LAST: Made from tough, waterproof, and crush-resistant materials. Manufactured in Sweden and programmed in the USA with the highest security standards.
What OAuth delegation does—and does not—guarantee
Delegation needs a clear authority boundary
OAuth access tokens are associated with an authorization grant and can represent access authorized for a user or workload. An agent should receive only the permissions needed for the task. Where supported, constrain the token by scope, resource, and action, and have the resource server check those constraints for each request.
OAuth token exchange standardizes a way to request and obtain tokens, including delegation and impersonation scenarios. It is a protocol building block, not proof that a particular system preserves the user’s intent. When exchanging tokens or passing delegated access between agents, validate that the subject, audience, scopes, and requested action match the intended task. IETF RFC 8693: OAuth 2.0 Token Exchange
Rank #2
- POWERFUL SECURITY KEY: The YubiKey 5C NFC is the most versatile physical passkey, protecting your digital life from phishing attacks. It ensures only you can access your accounts
- WORKS WITH 1000+ ACCOUNTS: Compatible with popular accounts like Google, Microsoft, and Apple. A single YubiKey 5C NFC secures 100+ of your favorite accounts, including email, password managers, and more
- FAST & CONVENIENT LOGIN: Plug in your YubiKey 5C NFC via USB and tap it, or tap it against your phone (NFC), to authenticate. No batteries, no internet connection, and no extra fees required
- MOST SECURE PASSKEY: Supports FIDO2/WebAuthn, FIDO U2F, Yubico OTP, OATH-TOTP/HOTP, Smart card (PIV), and OpenPGP. That means it’s versatile, working almost anywhere you need it
- PRIMARY & SPARE KEYS: Just like having a spare house key, we recommend buying two YubiKeys - one for daily use and one as a spare. That way you’ll never get locked out of your accounts
Client identity is not the same as user authorization
Client authentication establishes which application is requesting a token; user authorization establishes what access the user has granted. A confidential client’s identity alone does not authorize it to perform every action as a user. Keep those checks distinct in the design, and ensure the API enforces the permissions represented by the token.
OAuth does not neutralize agent risks
A compromised or manipulated agent can misuse whatever authority it has. OAuth does not prevent prompt injection, guarantee that tool calls match a user’s intent, or make broad scopes harmless. Restrict the agent’s permissions and enforce tool policies independently of the credential format.
Rank #3
- POWERFUL SECURITY KEY: The YubiKey 5 NFC is the most versatile physical passkey, protecting your digital life from phishing attacks. It ensures only you can access your accounts
- WORKS WITH 1000+ ACCOUNTS: Compatible with popular accounts like Google, Microsoft, and Apple. A single YubiKey 5 NFC secures 100+ of your favorite accounts, including email, password managers, and more
- FAST & CONVENIENT LOGIN: Plug in your YubiKey 5 NFC via USB and tap it, or tap it against your phone (NFC), to authenticate. No batteries, no internet connection, and no extra fees required
- MOST SECURE PASSKEY: Supports FIDO2/WebAuthn, FIDO U2F, Yubico OTP, OATH-TOTP/HOTP, Smart card (PIV), and OpenPGP. That means it’s versatile, working almost anywhere you need it
- PRIMARY & SPARE KEYS: Just like having a spare house key, we recommend buying two YubiKeys - one for daily use and one as a spare. That way you’ll never get locked out of your accounts
Revoking access and limiting exposure
OAuth tokens and refresh credentials
An authorization system may revoke access tokens or the refresh-token grant used to obtain them. A stolen access token can remain useful until it expires or the resource server otherwise rejects it; revocation is not necessarily immediate at every resource server. Shorter token lifetimes reduce that exposure window where supported, but there is no single lifetime established for all providers or deployments. Protect refresh credentials especially carefully because they can enable continued access.
API keys
A key may have no expiration and remain usable until it is disabled, deleted, or regenerated. Find the provider’s documented revocation action and understand which applications will stop working before rotating a shared key. Separate keys by application or workload where practical; that makes it easier to disable one integration without disrupting unrelated services. Google’s guidance covers key restrictions and management: Best practices for managing API keys and Manage API keys.
Rank #4
- POWERFUL SECURITY KEY: The Security Key NFC is the essential physical passkey for protecting your digital life from phishing attacks. It ensures only you can access your accounts.
- WORKS WITH 1000+ ACCOUNTS: Compatible with Google, Microsoft, and Apple. A single Security Key NFC secures 100 of your favorite accounts, including email, password managers, and more.
- FAST & CONVENIENT LOGIN: Plug in your Security Key NFC via USB-A and tap it, or tap it against your phone (NFC) to authenticate. No batteries, no internet connection, and no extra fees required.
- TRUSTED PASSKEY TECHNOLOGY: Uses the latest passkey standards (FIDO2/WebAuthn & FIDO U2F) but does not support One-Time Passwords. For complex needs, check out the YubiKey 5 Series.
- BUILT TO LAST: Made from tough, waterproof, and crush-resistant materials. Manufactured in Sweden and programmed in the USA with the highest security standards.
Credential-handling practices for agents
- Keep API secrets and OAuth refresh credentials in a secrets manager or platform-secure storage. Do not hardcode them, commit them to repositories, expose them in client-side code, or place broad credentials in prompts.
- Give each application or workload its own restricted credential where practical. Remove credentials that are no longer needed and monitor their use.
- Issue narrowly scoped, resource-restricted OAuth tokens with short lifetimes where the authorization server supports those controls. Avoid giving an agent a reusable refresh credential unless the architecture requires it; keep it outside the model context.
- Treat API keys as bearer secrets. Follow the provider’s delivery instructions, and do not place a key in a URL if the provider warns that URLs may be logged or scanned.
- Plan key rotation before an incident. Identify dependent workloads, test replacement credentials, and verify that the old key has actually been disabled.
For OAuth client authentication, RFC 9700 recommends asymmetric methods such as mutual TLS or signed JWT client assertions. These can avoid storing a sensitive symmetric client secret at the authorization server, but they bring key-management responsibilities of their own. IETF RFC 9700. Google also recommends securely storing OAuth credentials and user tokens, revoking tokens when they are no longer needed, and deleting them from systems: Google for Developers: Best Practices: Authorization Resources.
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Google Cloud’s Agent Registry MCP server uses OAuth 2.0 with IAM, requires a principal, and does not accept API keys. Its guidance recommends separate agent identities to control and monitor access. This illustrates one service’s design; it does not mean MCP universally requires OAuth. Google Cloud: Use the Agent Registry MCP server
Quick Recap
Best Value
- POWERFUL SECURITY KEY: The YubiKey 5 is a versatile physical passkey that protects your digital life from phishing attacks. It ensures only you can access your accounts.
- WORKS WITH 1000+ ACCOUNTS: Compatible with popular accounts like Google, Microsoft, and Apple. A single YubiKey 5 secures 100+ of your favorite accounts, including email, password managers, and more.
- FAST & CONVENIENT LOGIN: Plug in your YubiKey 5 via USB and tap it to authenticate. No batteries, no internet connection, and no extra fees required.
- MOST SECURE PASSKEY: Supports FIDO2/WebAuthn, FIDO U2F, Yubico OTP, OATH-TOTP/HOTP, Smart card (PIV), and OpenPGP. That means it’s versatile, working almost anywhere you need it.
- BUILT TO LAST: Made from tough, waterproof, and crush-resistant materials. Manufactured in Sweden and programmed in the USA with the highest security standards.
A practical decision checklist
- The agent acts for a user: use delegated OAuth or an equivalent system that can preserve the user’s identity and permissions.
- The API needs to distinguish workloads: use workload identity or OAuth client identities, with separate identities and policies where appropriate.
- The integration needs only a project-level credential: a provider-documented API key may fit, if it can be restricted to the intended API and environment.
- You cannot explain what the credential authorizes or how to revoke it: do not give it to the agent until those behaviors are clear.
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