Purpose, mechanics, and security angles of Federated Identity Brokers, Cloud Access Security Brokers, and API Gateways — plus their benefits and drawbacks.
1) Federated Identity Brokers (IdP Brokers)
Core function:
Act as a translator between identity providers (IdPs) and service providers (apps).
They handle authentication hand-off and token conversion across standards (SAML ↔ OIDC ↔ OAuth).
Where they sit:
Identity plane — between the user and the app.
Typical examples:
Azure AD B2B Federation, Auth0, Okta Identity Engine, Keycloak broker.
Primary use-cases
Single Sign-On across heterogeneous IdPs
M&A identity unification
Customer/partner access without duplicating accounts
Multi-protocol interoperability (SAML legacy to OIDC modern)
Benefits
Centralized SSO and identity governance
Protocol translation
Lower friction onboarding of external parties
Consistent policy enforcement (MFA, conditional access)
Drawbacks
Does not inspect app data or behavior
Not focused on threat defense beyond authentication policy
Broker compromise = catastrophic trust loss
Adds another identity dependency layer
2) Cloud Access Security Brokers (CASBs)
Core function:
Security enforcement point for SaaS/Cloud usage.
They monitor, inspect, restrict, and log data paths between enterprise users and cloud services.
Think: DLP, policy enforcement, risk scoring, shadow IT discovery, SaaS posture.
Where they sit:
Security control layer — between users and SaaS systems (forward proxy or API-mode).
Typical examples:
Netskope, Microsoft Defender for Cloud Apps, Skyhigh, Palo Alto Prisma, Cisco CASB.
Primary use-cases
Prevent data leaks (DLP)
Detect risky cloud usage/shadow IT
Control access based on device posture
Enforce SaaS security configuration baselines
Monitor data for regulatory exposure (PCI/GDPR)
Benefits
Strong data-level controls on cloud usage
Good visibility into SaaS applications
Enforcement of conditional policies
Helps with compliance (PII, secrets, IP)
Drawbacks
Limited depth on custom apps
API-mode coverage varies by SaaS vendor
Can produce false positives in DLP patterns
Latency and user friction if mis-tuned
Complex to operationalize — requires dedicated tuning and policies
3) API Gateways
Core function:
Manage and secure API traffic: routing, authentication, throttling, caching, protocol normalization.
Often the front-door for microservices or external-facing APIs.
Where they sit:
Application layer — between client/API consumer and backend services.
Typical examples:
Kong, Apigee, AWS API Gateway, Azure API Management, NGINX API Gateway.
Primary use-cases
Enforce API authentication/authorization
Rate limiting, throttling, quotas
Schema validation
Centralized logging/observability
Versioning and lifecycle control
Reverse proxy routing to services
Benefits
Security perimeter around APIs
Protects from OWASP API threats (injection, DDoS, enumeration)
Enables zero-trust service mesh patterns
Strong policy enforcement for API keys, JWT, mTLS
Operational controls for microservices
Drawbacks
Does not solve identity federation for SaaS/partners
No inherent data-level DLP or SaaS monitoring
Configuration mistakes can expose APIs
Can become a single bottleneck if not scaled properly
CategoryFederated Identity BrokersCASBsAPI GatewaysMain FocusAuthentication & federationData protection, SaaS usage controlAPI security, routing, service governanceLayerIdentity planeSecurity control/data planeApplication/API access planeProtectsIdentity & accessData in SaaS systems & cloud trafficAPIs and backend servicesTypical ControlsMFA, SSO, protocol translationDLP, risk scoring, device posture, SaaS configJWT validation, rate limits, schema enforcementVisibility TypeWhose identity is accessing whatHow users and data interact with SaaSHow APIs are called, by whom, and how muchThreat Model FocusStolen credentials, broken SSOData leakage, shadow IT, misconfig SaaSAPI attacks, traffic abuse, enumerationIntegrationsIdPs, SAML/OAuth/OIDCSaaS apps (via API) + proxyMicroservices, client apps, external systems
When They Overlap — and Why That Confuses People
All three may appear in cloud security architectures.
They all interact with authentication in some form:
Brokers perform federation logic
CASBs may embed identity awareness into policies
API gateways validate tokens/JWTs
But they operate at fundamentally different points: Identity vs Data vs Application traffic.
Rule of thumb:
Federation broker decides who you are and passes that identity along.
CASB decides what you are allowed to do with cloud services/data.
API Gateway decides how you may interact with backend APIs and services.
Strengths & Weaknesses in a Sentence
Federated Identity Broker:
Smooth federation and SSO across heterogeneous identity environments — but no deep data or application security.
CASB:
SaaS visibility and control with data-focused rules — but limited relevance to APIs or custom application logic.
API Gateway:
Strong API perimeter, routing and traffic control — but no SaaS governance or cross-domain identity brokerage.
Architectural Swap-ins (When to pick which)
Choose Identity Broker if:
You’re onboarding external suppliers, partners, customers
You have mixed SAML/OIDC ecosystems
You need centrally enforced access policy
Choose CASB if:
You must prevent data exfiltration from SaaS
Want shadow-IT discovery
Need compliance reporting for cloud data
Choose API Gateway if:
You expose APIs externally or run microservices
Want a clean, controlled API perimeter
Need versioning, throttling, authentication, telemetry
Concise Visual Stack (Text-based)
User/Entity │ [Federation Broker] │ — Identity established, token issued │ [CASB (optional data inspection/control)] │ [API Gateway] │ Backend App / Data / Services
