API Authentication & Authorization: Security Best Practices

Every protected API request raises two fundamental security questions:

Who or what is making this request?

What is that identity allowed to do?

The first question is handled by API authentication. The second is handled by API authorization.

Both are essential because modern APIs are accessed not only by people, but also by applications, service accounts, workloads, integrations and other machine identities. Weak authentication can allow an attacker to impersonate a legitimate identity. Weak authorization can allow a correctly authenticated identity to reach data, functions or resources it should never access. OWASP’s current API Security Top 10 includes Broken Authentication as well as several authorization-specific risks, including Broken Object Level Authorization and Broken Object Property Level Authorization.

A strong API access model therefore follows:

Identify → Authenticate → Authorize → Enforce → Protect Credentials → Review Access → Monitor → Improve

For the broader security model, see [Internal Link: API Security].

What Is API Authentication?

API authentication is the process of verifying the identity of the user, application, service or machine making an API request.

Authentication establishes confidence about who or what is requesting access before protected resources are made available.

Depending on the architecture and use case, authentication mechanisms can include:

• API keys
• Access tokens
• OAuth-based flows
• OpenID Connect
• JWT-based tokens
• Client certificates
• Service identities
• Workload identities

The correct mechanism depends on factors such as API sensitivity, whether the requester is human or machine, the deployment model and the level of identity assurance required.

Authentication should not be treated as proof that every subsequent action is legitimate. It establishes identity context. Authorization must still determine what that identity can actually do.

Human API Authentication

Human-facing applications may authenticate customers, employees, administrators or contractors through an identity provider.

OpenID Connect is specifically designed as an identity layer on top of OAuth 2.0 and enables clients to verify an end user’s identity based on authentication performed by an authorization server.

For human identities, security concerns include:

• Credential protection
• Session handling
• MFA where appropriate
• Token lifetime
• Account recovery
• Authentication monitoring

Machine-to-Machine Authentication

APIs are also called by:

• Applications
• Services
• Workloads
• Automation
• Service accounts

Machine authentication requires strong ownership and credential lifecycle management because these identities may operate continuously without interactive login.

What Is API Authorization?

API authorization is the process of determining which resources, functions and data an authenticated identity is permitted to access or modify.

Authorization answers questions such as:

• Which API can this identity call?
• Which endpoint can it access?
• Which record can it retrieve?
• Which function can it execute?
• Which properties can it read?
• Which fields can it modify?

This makes API authorization security much more granular than simply determining whether someone is logged in.

Resource-Level Authorization

Controls whether an identity can reach a particular API resource or service.

Object-Level Authorization

Controls access to individual records or objects.

OWASP identifies Broken Object Level Authorization as API1:2023 and notes that APIs receiving object identifiers should implement object-level authorization checks for the requested resource.

Function-Level Authorization

Restricts privileged operations such as administrative or management functions to appropriate identities.

Property-Level Authorization

Controls which fields within an object an identity can read or modify.

OWASP’s API3:2023 addresses cases where an authenticated user can access sensitive properties that should remain restricted.

For the full OWASP risk model, see [Internal Link: OWASP API Security].

API Authentication vs Authorization

API Authentication	API Authorization
Confirms identity	Determines permissions
Answers “Who are you?”	Answers “What can you do?”
Uses identity proof or credentials	Uses roles, attributes and policies
Establishes identity context	Controls resources and actions
Failure can enable impersonation	Failure can enable excessive access

Why the Difference Matters

Imagine a customer successfully authenticates to an online service.

That authentication proves the system has accepted the customer’s identity.

It should not mean the customer can:

• View another customer’s records
• Change another user’s account
• Delete resources belonging to someone else
• Call administrator-only functions
• Read restricted properties

That requires separate authorization decisions.

The key principle is:

Authentication without authorization is incomplete API security.

How API Authentication and Authorization Work Together

A secure access flow can be represented as:

Request → Identity Verification → Authentication → Authorization Policy → API Resource → Response

Step 1 — Present Credentials

The requester provides an appropriate credential or identity proof.

Step 2 — Verify Identity

The authentication system determines whether that proof is valid.

Step 3 — Establish Authentication Context

The system establishes context such as:

• Subject identity
• Authentication method
• Token validity
• Client identity

Step 4 — Evaluate Permissions

The authorization layer evaluates:

• Roles
• Entitlements
• Attributes
• Resource ownership
• Policies
• Context

Step 5 — Authorize the Resource or Action

The system determines whether the requested action is allowed.

Step 6 — Log the Decision

Relevant authentication and authorization events should be available for security monitoring and investigation.

Strong API access security requires both reliable identity verification and permissions appropriate to the requested resource.

API Authentication Methods

There is no single authentication method that is universally best for every API.

API Keys

API keys are often used to identify applications or consumers.

They can be useful for controlled machine access, but their security depends heavily on how they are stored, scoped, rotated and revoked.

Token-Based Authentication

Tokens can provide temporary or scoped credentials without repeatedly transmitting a primary credential.

OAuth

OAuth 2.0 is an authorization framework designed to allow applications to obtain limited access to protected HTTP resources. RFC 6749 describes the model as enabling limited access either on behalf of a resource owner or on the application’s own behalf.

OpenID Connect

OpenID Connect adds an authentication and identity layer on top of OAuth 2.0.

Client Certificates

Client certificates can provide strong service or workload identity in architectures where certificate lifecycle management is mature.

Service and Workload Identities

Cloud-native and distributed environments increasingly require dedicated non-human identities rather than shared user credentials.

API Keys Security

API keys security depends less on the format of the key and more on how the credential is managed.

Common API Key Risks

Risks include:

• Hard-coded keys
• Keys committed to public repositories
• Shared credentials
• Excessively long lifetime
• Broad permissions
• Keys written to logs
• Missing rotation
• No clear owner

API Key Security Best Practices

Organisations should:

• Store keys in approved secrets-management systems
• Avoid exposing keys in client-side code
• Scope permissions where possible
• Rotate credentials
• Revoke compromised keys
• Assign clear ownership
• Monitor usage
• Remove unused keys

API Keys vs Identity

An API key may identify an application or consumer, but it does not automatically establish strong human identity assurance.

A shared key can show that a request came from someone possessing the secret without proving which individual person used it.

That distinction becomes important in environments requiring accountability.

OAuth API Security

OAuth 2.0 is primarily an authorization framework, not a general-purpose identity protocol. OpenID Connect provides the identity layer when authentication of an end user is required.

OAuth Security Benefits

Properly designed OAuth deployments can support:

• Scoped access
• Delegated authorization
• Separation from primary user credentials
• Limited access tokens
• Application-specific permissions

OAuth Security Risks

Risks can include:

• Insecure redirect handling
• Excessive scopes
• Token leakage
• Weak client configuration
• Poor token storage
• Excessive token lifetime

The current IETF Best Current Practice for OAuth 2.0 security is RFC 9700, which updates earlier OAuth security guidance and deprecates some modes considered insecure or weaker in modern deployments.

OAuth Security Best Practices

At a high level:

• Minimise scopes
• Validate tokens correctly
• Use secure authorization flows
• Protect redirects
• Use encrypted transport
• Protect refresh tokens
• Revoke access that is no longer required
• Follow current OAuth security guidance rather than relying only on older implementation patterns

For security-sensitive deployments, current standards and provider guidance should be reviewed during implementation.

JWT Security for APIs

JWTs are commonly used to carry signed claims representing identity or authorization context.

A JWT is a format. Using the format does not automatically make authentication secure.

What a JWT Commonly Contains

Claims can include:

• Subject
• Issuer
• Audience
• Expiration
• Identity or authorization-related attributes

Common JWT Security Risks

Potential weaknesses include:

• Improper signature validation
• Accepting expired tokens
• Incorrect issuer validation
• Incorrect audience validation
• Excessive token lifetime
• Sensitive information placed in the payload
• Weak signing-key management

JWT Security Best Practices

Applications should:

• Verify signatures
• Validate the expected issuer
• Validate the intended audience
• Enforce expiration
• Protect signing keys
• Avoid placing unnecessary sensitive data in tokens
• Reject tokens that do not meet the expected security policy

JWT is a token format, not a complete authentication or authorization strategy.

The surrounding identity, key-management and authorization design determines whether the implementation is secure.

API Token Security

Token security applies to access tokens, refresh tokens, session tokens and service tokens.

Scope Tokens Carefully

Grant only permissions required for the intended use.

Limit Token Lifetime

Shorter validity periods can reduce the window in which a stolen token remains useful.

Protect Tokens in Storage and Transit

Tokens should be treated as security-sensitive credentials.

Rotate and Revoke Tokens

Organisations need processes for responding to compromise and ending unnecessary access.

Monitor Token Use

Unexpected locations, APIs or request patterns can indicate misuse.

Avoid Token Exposure in Logs and URLs

Security telemetry should not create a new credential-leakage path.

API Access Control Models

API access control can be implemented using different policy models.

Role-Based Access Control

Permissions are associated with roles such as:

• Customer
• Support agent
• Manager
• Administrator

RBAC can be straightforward but may become overly broad when roles accumulate many unrelated permissions.

Attribute-Based Access Control

ABAC evaluates attributes associated with:

• Identity
• Resource
• Environment
• Action

This can support more contextual decisions.

Policy-Based Access Control

Explicit policies define how authorization decisions should be made.

Ownership-Based Access

Useful where an identity should access only objects it owns or is assigned.

Context-Aware Access

Authorization may also consider context such as:

• Time
• Device
• Location
• Risk
• Authentication strength

These models can be combined according to the environment.

Fine-Grained API Authorization

Strong authorization should evaluate:

Identity → Action → Resource → Context

Object-Level Controls

Determine whether the identity can access a particular object.

Function-Level Controls

Restrict high-risk operations.

Property-Level Controls

Restrict specific fields or attributes.

Contextual Controls

Consider additional business or security context where relevant.

The key principle is:

Authorization should be enforced for the specific resource and action, not assumed from successful authentication.

This is especially important where a single API serves users with different roles and levels of privilege.

Least Privilege in API Access Security

Least privilege means giving each human or machine identity only the API access necessary for its legitimate function.

It should apply to:

• Users
• Administrators
• Applications
• Service accounts
• Workloads
• Partners
• Third-party integrations

Avoid Broad API Scopes

Do not grant broad access simply because it is easier to manage initially.

Limit Privileged Functions

Administrative actions should be restricted to identities with a clear need.

Remove Unused Entitlements

Permissions often accumulate after role, application or organisational changes.

Review Access Periodically

Access that was valid when granted may not remain valid indefinitely.

Use Time-Limited Access Where Appropriate

Temporary or high-risk activities may justify access with an explicit expiration.

Least privilege is therefore not merely an initial configuration decision. It must be maintained across the identity lifecycle.

API Identity Management

API identity management must account for several different identity populations.

Human Identities

Includes:

• Customers
• Employees
• Contractors
• Administrators

Application Identities

Applications may consume APIs directly on behalf of users or their own business processes.

Service Accounts

Services and automation frequently operate under dedicated identities.

Workload Identities

Cloud-native services may require identity independently of long-lived static credentials.

External Identities

Partner organisations and third-party applications may require controlled access.

Across all categories, organisations need consistent:

• Identification
• Ownership
• Authentication
• Credential lifecycle
• Access assignment
• Review

Machine Identities and API Authentication

Machine identities are particularly important because they can generate large amounts of API activity continuously.

Risks include:

• Shared service accounts
• Hard-coded secrets
• Long-lived credentials
• Unknown ownership
• Excessive permissions
• Dormant service accounts

Give Every Machine Identity Clear Ownership

Every significant non-human identity should have an accountable owner or responsible team.

Avoid Shared Credentials

Shared credentials reduce accountability and complicate revocation.

Apply Least Privilege

Machine permissions should match actual service requirements.

Rotate Credentials

Credentials should have defined lifecycle processes.

Monitor Behavior

Unexpected changes in API usage can indicate compromise or configuration problems.

Review Machine Access

SecurEnds currently supports governance of service accounts and AI accounts, including visibility into what those non-human identities can access and recurring access reviews.

Machine authentication therefore needs both technical credential security and access governance.

Broken Authentication in API Security

Broken authentication refers to weaknesses that allow attackers to bypass authentication controls or impersonate legitimate users or clients.

OWASP identifies Broken Authentication as API2:2023 and notes that implementation flaws can allow authentication tokens to be compromised or identities to be assumed improperly.

Risks can include:

• Weak credential handling
• Improper token validation
• Credential stuffing
• Missing rate controls
• Insecure authentication flows
• Long-lived compromised credentials

How to Reduce Broken Authentication Risk

Use:

• Standardised authentication
• Strong credential protection
• Correct token validation
• Rate limiting
• Secure secrets management
• Monitoring
• MFA where appropriate
• Secure machine authentication

For the broader OWASP model, see [Internal Link: OWASP API Security].

Broken Authorization in API Security

Broken authorization occurs when an authenticated identity can access resources, properties or functions beyond its intended permissions.

Broken Object-Level Authorization

A user can access an object belonging to another identity.

Broken Function-Level Authorization

An ordinary user can perform a privileged function.

Broken Property-Level Authorization

A user can access or change fields that should remain restricted.

Excessive Permissions

The access may be technically legitimate but broader than the identity actually needs.

This is a governance problem rather than necessarily a coding vulnerability.

How to Reduce Broken Authorization Risk

Organisations should:

• Deny by default
• Enforce authorization server-side
• Check permissions at the relevant resource
• Use fine-grained policies
• Test multiple roles
• Apply least privilege
• Periodically review entitlements

OWASP’s API Top 10 separates object-, property- and function-level authorization weaknesses because authorization needs to operate at multiple levels.

Authentication and Authorization Testing

Testing should validate authentication and authorization independently.

Authentication Tests

Check:

• Missing credentials
• Invalid credentials
• Expired credentials
• Incorrect tokens
• Revoked credentials
• Token-validation behaviour

Authorization Tests

Check:

• Cross-user object access
• Role boundaries
• Administrative functions
• Property access
• Service-account permissions

Test Multiple Identities

Include representative identities such as:

• Standard user
• Privileged user
• Application
• Service account

Testing with only one administrator account can easily miss permission-boundary weaknesses.

For the complete methodology, see [Internal Link: API Security Testing].

Authentication and Authorization Monitoring

Runtime monitoring should provide visibility into access-related events without turning every failed request into an incident.

Useful signals include:

• Authentication failures
• Invalid-token events
• Authorization denials
• Privileged actions
• API-key usage
• Service-account activity
• Unusual endpoint access

Why Identity Context Matters

A valid request can still be suspicious.

For example, a service account may successfully authenticate but suddenly call administrative APIs outside its normal operating pattern.

Security teams need both:

What did the identity do?

and

What was the identity expected or entitled to do?

For runtime visibility, see [Internal Link: API Security Monitoring] and [Internal Link: API Threat Detection].

Authentication and Authorization in Zero Trust API Security

Zero Trust principles are particularly relevant to API access because network location should not automatically establish trust.

Use the model:

Verify Identity → Evaluate Access → Apply Least Privilege → Monitor Continuously

Never Trust Network Location Alone

An internal request should still be authenticated and appropriately authorized.

Authenticate Human and Machine Identities

Both identity types can be compromised.

Authorize the Specific Resource

Access decisions should reflect what is being requested.

Minimize Privileges

Limit the potential blast radius of compromised identities.

Continuously Evaluate Activity

Successful authentication at the start of a session or workflow does not mean every later request is harmless.

API Authentication and Authorization Across the Lifecycle

API access controls need to follow both the API lifecycle and the identity lifecycle.

Design

Define identity populations and authorization models.

Development

Implement authentication, resource authorization and credential protection.

Testing

Validate authentication and permission boundaries.

Deployment

Protect production credentials and configure access controls correctly.

Runtime

Monitor access decisions and unusual identity behaviour.

Role or Access Changes

Update permissions when identities change roles or business purpose.

Retirement

Revoke:

• API keys
• Tokens
• Service credentials
• Associated entitlements

The key takeaway is:

API access security must follow both the API lifecycle and the identity lifecycle.

API Authentication & Authorization Best Practices

Use the following practices to strengthen API authentication security and authorization:

• Use standardised authentication mechanisms
• Separate authentication from authorization
• Enforce authorization server-side
• Apply object- and function-level checks
• Restrict sensitive properties
• Apply least privilege
• Minimise OAuth scopes
• Validate JWT signatures and claims
• Protect API keys and tokens
• Use appropriately short-lived credentials where practical
• Secure machine identities
• Rotate and revoke credentials
• Monitor authentication and authorization events
• Review access periodically
• Remove stale permissions
• Test multiple roles and identity types

For broader controls, see [Internal Link: API Security Best Practices].

API Authentication & Authorization Checklist

Authentication

• Protected APIs require authentication.
• Authentication mechanisms are standardised.
• Expired credentials are rejected.
• Tokens are properly validated.
• Machine identities are authenticated.

API Keys and Tokens

• Keys are not hard-coded.
• Tokens are appropriately scoped.
• Credentials have accountable owners.
• Rotation processes exist.
• Revocation processes exist.

Authorization

• Object-level authorization is enforced.
• Function-level authorization is enforced.
• Property-level controls are reviewed.
• Privileged functions are restricted.

Least Privilege

• Roles contain only necessary permissions.
• Excessive access can be identified.
• Stale access is removed.

Testing

• Authentication failures are tested.
• Multiple roles are tested.
• Cross-user object access is tested.
• Privilege boundaries are tested.

Monitoring

• Authentication failures are logged.
• Authorization denials are monitored.
• Privileged actions are visible.
• Machine identities are included.

Governance

• Access owners are identified.
• Access reviews occur.
• Remediation decisions are tracked.

Common API Authentication and Authorization Mistakes

Treating Authentication as Authorization

A valid identity does not imply unrestricted permission.

Using API Keys as the Only Security Control

A key may identify a client without providing sufficient user identity or fine-grained authorization context.

Using Overly Broad OAuth Scopes

Broad scopes undermine limited delegation.

Failing to Validate JWT Claims Properly

Signature verification alone is insufficient if issuer, audience or expiration is ignored.

Using Long-Lived Credentials Without Rotation

Long-lived compromised credentials can extend an attacker’s access window.

Hard-Coding Secrets

Embedded credentials are harder to control and rotate safely.

Enforcing Authorization Only at the API Gateway

Fine-grained resource access often requires application context.

Ignoring Object-Level Permissions

Authenticated users should not automatically access arbitrary object identifiers.

Giving Service Accounts Excessive Access

Machine identities can become high-impact attack paths.

Failing to Review Entitlements

Legitimate access can become inappropriate over time.

Ignoring Stale Accounts and Credentials

Unused access should not persist indefinitely.

Logging Tokens or Secrets

Monitoring data should not expose reusable credentials.

How Identity Governance Strengthens API Access Security

Authentication proves identity. Authorization enforces permissions. Identity governance helps determine whether those permissions should have been granted and whether they should still exist.

A useful model is:

Identity → Role → Entitlement → Authorization → API Resource

Understand Who Has Access

Organisations need visibility into users, applications and machine identities.

Gain Entitlement Visibility

Role names alone may not show the actual permissions an identity possesses.

Review User Access

Periodic reviews help determine whether permissions remain aligned with current responsibilities.

SecurEnds describes user access reviews as recurring processes designed to verify that users retain the minimum necessary access.

Review Application and Service Access

Non-human identities require the same governance principle.

SecurEnds currently provides visibility into the access held by service accounts and other non-human identities and supports recurring reviews across their lifecycle.

Identify Excessive Permissions

Access can accumulate after role changes, projects and system migrations.

Govern Privileged Access

High-impact entitlements should receive stronger scrutiny.

Certify Access

Business owners should periodically confirm continued need.

Remediate Unnecessary Access

Review findings should result in permission removal or adjustment.

Manage Identity Lifecycle

Access should change when people, applications or services change role, purpose or status.

The critical point is:

A perfectly functioning authorization engine can still permit risky access if the underlying role or entitlement is inappropriate.

How SecurEnds Supports API Access Governance

SecurEnds complements technical API authentication and API authorization by providing governance over the identities and entitlements behind those access decisions.

Its verified capabilities include user access reviews, entitlement review, recurring certification and governance of non-human identities such as service accounts. SecurEnds’ non-human identity offering provides visibility into what those identities can access and brings their permissions into recurring review processes.

The role is distinct from authentication infrastructure itself.

API authentication and authorization technologies enforce access during API interactions. Identity governance complements those controls by helping organisations ensure users and applications retain only appropriate access to connected resources.

This supports least privilege, access certification and remediation without treating identity governance as a replacement for OAuth, token validation or API-level authorization.

How to Build a Strong API Authentication and Authorization Strategy

Step 1 — Identify Human and Machine Identities

Document all significant identity types accessing APIs.

Step 2 — Classify APIs and Resources

Identify sensitive data, privileged functions and high-risk resources.

Step 3 — Define Authentication Requirements

Select authentication controls according to identity type and risk.

Step 4 — Design the Authorization Model

Define who can perform which action against which resource.

Step 5 — Map Roles and Entitlements

Connect business roles and application permissions to actual access.

Step 6 — Apply Least Privilege

Remove unnecessary permissions and overly broad scopes.

Step 7 — Secure Keys, Tokens and Credentials

Establish secure storage, ownership, rotation and revocation.

Step 8 — Test Authentication and Authorization Separately

Do not assume one validates the other.

Step 9 — Monitor Access Decisions

Collect authentication, denial and privileged-access signals.

Step 10 — Review and Certify Access

Periodically confirm continued business need.

Step 11 — Revoke Unnecessary Access and Credentials

Remove stale permissions, keys and machine access.

Step 12 — Continuously Reassess

Update controls when APIs, identities, roles and risks change.

The final model is:

Identify → Authenticate → Authorize → Protect → Monitor → Review → Remediate

Build API Access Security Around Identity and Permission

Strong API authentication security and API authorization security require more than choosing an authentication protocol.

The complete model combines:

Identity verification + secure credentials + fine-grained authorization + least privilege + monitoring + access governance

API keys, OAuth, OpenID Connect and JWTs can all play roles in secure API access when they are implemented and managed correctly. OAuth provides delegated authorization, while OpenID Connect provides an authentication layer on top of OAuth 2.0. Current OAuth security guidance also continues to evolve, making implementation practices as important as protocol selection.

The distinction to preserve is:

API authentication determines who or what is making a request, and authorization determines what that identity can do. Identity governance adds the ongoing oversight needed to ensure that the roles and entitlements behind those decisions remain appropriate.

For technical placement of these controls, see [Internal Link: API Security Architecture]. For testing, see [Internal Link: API Security Testing].

Frequently Asked Questions

What is API authentication?

API authentication is the process of verifying the identity of the person, application, service or machine making an API request.

It can use mechanisms such as API keys, tokens, OpenID Connect, certificates or workload identities depending on the use case.

What is API authorization?

API authorization determines what an authenticated identity can access or do.

It can control API resources, individual objects, privileged functions and specific data properties.

What is the difference between API authentication and authorization?

Authentication answers:

Who are you?

Authorization answers:

What are you allowed to do?

An identity can successfully authenticate while still being denied access to particular resources or functions.

Are API keys secure for authentication?

API keys can be appropriate for some application or machine-identification scenarios when securely stored, scoped, rotated and monitored.

However, a key does not automatically provide strong human identity assurance or fine-grained authorization. It should be used according to the security requirements of the API rather than treated as a universal authentication solution.

How does OAuth improve API security?

OAuth allows applications to obtain limited, delegated access to protected resources without requiring the user’s primary credentials to be shared with the application.

Security still depends on correct implementation, limited scopes, secure token handling and current OAuth security guidance.

What are the main JWT security risks?

Common JWT risks include improper signature validation, accepting expired tokens, failing to validate issuer or audience, overly long token lifetimes, weak key management and placing unnecessary sensitive data in token payloads.

JWT is only a format; secure token processing and authorization remain essential.

How does identity governance improve API access security?

Identity governance helps organisations determine whether users, applications and machine identities should continue to hold the permissions that allow access to connected resources.

Access reviews, entitlement visibility, least-privilege governance and remediation complement technical API authorization by addressing stale or excessive underlying permissions. SecurEnds currently supports recurring access reviews for both human and non-human identities.