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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsStart with the identity your agent needs to present. If it must access a person’s data under that person’s authorization, use a delegated authorization design such as OAuth. If it runs unattended, give it a workload identity and narrowly assigned permissions where the API supports that approach. An API key may identify an application or project for access controls, quota, or usage attribution, but it is not automatically a substitute for user identity or secure authorization.
What does the agent need to identify?
An AI agent is not an authentication method. It is a client that calls an API, and its credential should represent the right principal: a user who granted access, a non-human workload, or an application or project. The target API and identity provider determine which methods are available and what each credential means.
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- User: The agent acts with delegated access to an individual’s resources.
- Workload: The agent runs without an end user and acts as a service or workload principal.
- Application or project: The API uses a key to identify the calling software, attribute usage, or control quota.
OAuth and API keys represent different things
OAuth access tokens carry an authorization grant
OAuth is an authorization framework for obtaining access to a protected resource. An access token represents an authorization grant, whose scope, duration, and other attributes are determined by the authorization server and resource server; OAuth itself does not define every API’s business permissions. See the IETF’s RFC 6749.
This makes OAuth a natural fit when access needs to reflect a user’s authorization or a service’s access policy. The token’s actual permissions, audience, lifetime, and refresh or revocation behavior depend on the provider’s implementation.
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API keys often identify an application or project
Semantics differ by provider. As a concrete Google Cloud example, its API-key guidance says keys identify the calling project—the application or site—and can support project-level authorization, usage attribution, quota control, and log filtering. Google also says its keys do not identify individual users and are not a secure way to authorize access. Those statements describe Google Cloud’s guidance, not every API’s key model. See Why and when to use API keys.
Google Cloud’s broader authentication overview distinguishes an API key not bound to a service account, which identifies a project for billing and quota, from an OAuth client ID used when an application accesses end-user-owned resources. The overview describes a service-account-bound API-key feature as a preview; do not assume it is generally available or portable to other providers. See Authentication for Google Cloud APIs and services.
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Choose for delegated access or unattended work
When the agent acts for a person
Use an authorization flow that represents the person’s grant when the agent needs access to that person’s resources. Check that the API can limit the grant to necessary permissions and resources, and determine how access is withdrawn. A shared project key generally cannot express which individual authorized a particular action.
When the agent runs as a workload
An unattended agent should normally act as a non-human workload principal, with only the access it needs. Google Cloud describes service accounts as non-human identities for workloads without end-user involvement and recommends using service-account keys only when no viable alternative exists. These are Google Cloud recommendations; other platforms have their own workload identity mechanisms. See Google Cloud’s service-account security guidance.
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On Google Cloud, Application Default Credentials (ADC) lets client libraries locate credentials according to the runtime environment. Its behavior and available options are platform-specific; see How Application Default Credentials works.
Compare the options against your actual requirements
| Decision factor | What to establish |
|---|---|
| Identity represented | Does the API need to know the user, a workload or service principal, or only the application/project? |
| Permission limits | Can access be narrowed by scope, resource, operation, audience, and policy? |
| Exposure and replay | Is possession enough to use the credential? Can the credential be sender-constrained, and how does it reach the agent runtime? |
| Lifetime and revocation | When does it expire? Can it be refreshed or revoked, and how quickly does revocation take effect? |
| Auditability | Will logs identify the user, workload, project, or only a shared credential? |
| Operational fit | Does the API support the method? How will credentials be stored, rotated, onboarded, and attributed for quota? |
These are comparison axes, not a universal ranking of protocols. The practical choice depends on the API, identity provider, required permissions, and the way credentials are issued and managed.
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Protect tokens and keys as credentials
For OAuth bearer tokens
A bearer token is usable by whoever possesses it; the holder does not have to prove possession of cryptographic key material. The IETF identifies preventing unintended disclosure as the primary security concern for bearer tokens. Send them only over TLS, validate the server’s identity, keep them out of URLs, and protect storage and logs. Where supported, restrict audience and scope and use short-lived tokens. RFC 6750 says authorization servers should issue short-lived bearer tokens and gives one hour or less as guidance, particularly for browser or other leakage-prone environments; this is not a universal required lifetime for agent tokens. See RFC 6750.
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When both client and server support it, sender-constrained tokens can reduce the risk that a stolen token works on its own. RFC 8705 describes certificate-bound OAuth tokens, which require the corresponding certificate’s private key. This adds certificate and key management. RFC 9700 recommends asymmetric client authentication, such as mutual TLS or signed JWTs, when feasible; support varies by API and agent deployment. See RFC 8705 and the January 2025 OAuth 2.0 Security Best Current Practice.
For API keys
Keep keys out of client code, source repositories, and URL query parameters. Restrict each key to its intended APIs and environment, remove unused keys, monitor use, and rotate keys when appropriate. Google Cloud recommends these controls and generally advises migrating production authorization to IAM policies and short-lived service-account credentials, with a documented Gemini API-specific exception. Provider features and recommendations differ. See Google Cloud’s API-key best practices.
Quick Recap
Decision checklist
- Confirm which authentication methods the target API supports.
- Decide whether the agent acts for a user or as an unattended workload; use an application/project key only where that identity and its permitted role fit the API.
- Identify the minimum required permissions and whether the method can constrain them to the right resources and audience.
- Check what the API’s logs attribute to the credential and whether that is enough for audit and quota tracking.
- Document where credentials are stored, how they are protected from logs and client exposure, and how quickly each can expire or be revoked after compromise.
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