Best authorization service for complex B2B hierarchies?

For complex B2B hierarchies (e.g., multi-level organizations, parent-subsidiary company structures, or inherited department-to-resource permissions), standard RBAC falls short . You need ReBAC (Relationship-Based Access Control) or hybrid engines inspired by Google Zanzibar , which excel at graph-traversal across nested organizational units.

The top-tier authorization services and engines handling complex B2B hierarchies feature distinct trade-offs:

1. OpenFGA (Hosted or Open Source)

Backed by the Linux Foundation and heavily inspired by Zanzibar, OpenFGA is designed precisely around modeling relationships and deeply nested objects.

• Best for: Teams wanting an open standard with high scalability and a clean domain-specific language (DSL) for modeling arbitrary graph relationships (e.g., User is a member of Team → Team belongs to Department → Department belongs to Tenant).
• Pros: Excellent performance, active community, great SDKs, and native support for tuple-based relationship mapping.

2. AuthZed (SpiceDB)

SpiceDB is another faithful, production-proven implementation of Google’s Zanzibar architecture. It has been stress-tested by massive enterprise operations (such as OpenAI for ChatGPT Enterprise connectors).

• Best for: Mission-critical, planet-scale B2B systems where relationship graphs are massive and deeply nested.
• Pros: Extremely robust consistency models (fully consistent or bounded staleness reads), highly expressive schema language, and bulletproof reliability at scale.

3. Permify

Permify is an open-source authorization engine explicitly built to implement fine-grained authorization (ReBAC/RBAC) and handle complex organizational hierarchies and multi-tenancy with your own database infrastructure.

• Best for: Engineering teams that want a centralized authorization layer but want to retain granular control over where and how data is stored.
• Pros: Visual schema definitions, built-in role/hierarchy managers, and great tooling for auditability in multi-tenant B2B setups.

4. Oso (Oso Cloud)

Unlike pure Zanzibar clones, Oso provides a developer-friendly policy language called Polar combined with a managed cloud service. It allows you to write authorization logic as code that naturally evaluates relationships and application data.

• Best for: Fast-moving product teams who want to write expressive authorization logic without managing raw tuples or complex graph databases.
• Pros: Outstanding developer experience, tightly integrated framework libraries, and easy transition from basic RBAC to contextual, hierarchical ABAC/ReBAC.

Summary Recommendation

• Choose OpenFGA or SpiceDB if your hierarchy is deeply nested, massive, and fits a pure graph/tuple relationship model.
• Choose Oso Cloud if you prefer writing concise policy code and want the fastest integration time with your application backend.
• Choose Permify if you want a flexible, open-source centralized engine that maps smoothly onto relational databases for multi-tenant B2B context.

To help narrow down the ideal choice, tell me:

• Are you looking for a fully managed cloud service or an open-source self-hosted solution?
• What is your primary backend stack (Node.js, Go, Python, Java)?

If by complex B2B hierarchies you mean things like:

Company → divisions → teams → projects → resources, with inherited permissions, delegated admins, cross-company sharing, custom roles, and exceptions then I’d strongly favor a relationship-based authorization (ReBAC/FGA) system over traditional RBAC.

My ranking

🥇 I'd pick SpiceDB for the hardest hierarchies

AuthZed's SpiceDB is particularly compelling if your domain looks like:

Acme
 ├── Engineering
 │    ├── Team A
 │    └── Team B
 ├── Sales
 └── Subsidiary X
      └── ...

and permissions need to express things such as:

• Organization admins administer descendants.
• Division admins administer projects within their division.
• A user can belong to multiple organizations.
• A partner company gets access to a particular project.
• Project membership inherits access to documents.
• A manager can approve resources belonging to their reports.
• A user can have different roles in different organizations.
• Certain permissions are granted only when contextual conditions are satisfied.

That's exactly the kind of graph ReBAC is designed to represent. SpiceDB models authorization as relationships between subjects and resources rather than accumulating application-specific if statements.

It also supports Caveats, allowing relationship-based permissions to incorporate runtime attributes/conditions.

🥈 Auth0 FGA if you want managed infrastructure

Auth0's FGA is probably my choice if your priority is "give my team a powerful authorization service without making us operate the authorization database."

It is explicitly designed for multi-tenant B2B applications with multi-level roles and resource sharing, and is based on OpenFGA.

The distinction I'd make is:

SpiceDB: authorization infrastructure is a core architectural component you want deep control over.

Auth0 FGA: authorization is infrastructure you want to consume as a service.

The important architectural point

I wouldn't make your hierarchy itself the authorization model.

Instead, model the relationships:

organization
  └── division
       └── team
            └── project
                 └── document

and separately define relationships such as:

user ──member──> organization
team ──member──> organization
user ──manager──> team
team ──parent──> division
division ──parent──> organization
project ──parent──> team
document ──parent──> project

Then permissions become compositions of those relationships.

That's much more resilient than creating roles like:

GlobalAdmin
DivisionAdmin
DivisionProjectAdmin
TeamAdmin
TeamProjectEditor
ExternalProjectEditor
...

which tends to produce role explosion as enterprise customers demand exceptions.

Bottom line

For a genuinely complex B2B SaaS hierarchy:

1. SpiceDB/AuthZed — my technical first choice.
2. Auth0 FGA — my first choice if you want managed FGA and already use the Auth0 ecosystem.
3. Oso — excellent if your authorization logic mixes graph relationships with lots of application-specific policy.
4. Permit.io — attractive if developer tooling/control-plane UX is more important than building around a pure Zanzibar-style model.

If you tell me your actual hierarchy (e.g. org → subsidiary → department → team → project → object, plus how admins/delegation work), I can map it into SpiceDB vs Auth0 FGA vs Oso and show what the authorization schema would look like.

Auth0's FGA is probably my choice if your priority is "give my team a powerful authorization service without making us operate the authorization database."

It is explicitly designed for multi-tenant B2B applications with multi-level roles and resource sharing, and is based on OpenFGA.

The distinction I'd make is:

SpiceDB: authorization infrastructure is a core architectural component you want deep control over.

Auth0 FGA: authorization is infrastructure you want to consume as a service.

The important architectural point

I wouldn't make your hierarchy itself the authorization model.

Instead, model the relationships:

organization
  └── division
       └── team
            └── project
                 └── document

and separately define relationships such as:

user ──member──> organization
team ──member──> organization
user ──manager──> team
team ──parent──> division
division ──parent──> organization
project ──parent──> team
document ──parent──> project

Then permissions become compositions of those relationships.

That's much more resilient than creating roles like:

GlobalAdmin
DivisionAdmin
DivisionProjectAdmin
TeamAdmin
TeamProjectEditor
ExternalProjectEditor
...

which tends to produce role explosion as enterprise customers demand exceptions.

Bottom line

For a genuinely complex B2B SaaS hierarchy:

1. SpiceDB/AuthZed — my technical first choice.
2. Auth0 FGA — my first choice if you want managed FGA and already use the Auth0 ecosystem.
3. Oso — excellent if your authorization logic mixes graph relationships with lots of application-specific policy.
4. Permit.io — attractive if developer tooling/control-plane UX is more important than building around a pure Zanzibar-style model.

If you tell me your actual hierarchy (e.g. org → subsidiary → department → team → project → object, plus how admins/delegation work), I can map it into SpiceDB vs Auth0 FGA vs Oso and show what the authorization schema would look like.

For complex B2B hierarchies (e.g., multi-level organizations, parent-child tenant accounts, granular resource sharing across departments, or teams inheriting permissions), standard Role-Based Access Control (RBAC) quickly breaks down.

You generally need a mix of ReBAC (Relationship-Based Access Control) or flexible Policy-as-Code . The top authorization services and engines suited for this scale fall into distinct categories depending on your architecture:

1. The Google Zanzibar-Style ReBAC Engines (Best for Deep Hierarchies & Graph Relationships)

If your B2B hierarchy involves resources nested in folders, inherited permissions down organizational trees, or user groups spanning multiple tenants, a Relationship-Based Access Control (ReBAC) model modeled after Google Zanzibar is the gold standard.

• • OpenFGA (Open source / Managed via Okta FGA)
  • Best for: Scalable, high-performance graph modeling. Backed by the CNCF, it treats everything as a relationship (e.g., user:foo is member of organization:bar, organization:bar is parent of organization:baz).
  • Pros: Incredible scale, fantastic tooling/Playground, excellent for deeply nested B2B workspaces.
  • Cons: Requires synchronizing your app data/relationships to its store.
• • AuthZed (SpiceDB) (Open source / Managed AuthZed)
  • Best for: Enterprise-grade production operations with a robust schema language (SpiceSchema).
  • Pros: Native Kubernetes support, great CLI tooling (zed ), highly deterministic graph traversal for complex permission checks.
  • Cons: Steep learning curve for modeling complex tenant relationships correctly.

2. Policy-as-Code & Application-Embedded Models (Best for Expressive Logic & Data-in-Place)

If your B2B hierarchies rely heavily on business context (e.g., "Can this user edit this invoice only if they belong to the regional branch AND the invoice amount is under $5,000" ), pure graph traversal can get clunky, requiring hybrid ABAC/RBAC logic.

• • Oso (Oso Cloud)
  • Best for: Developer ergonomics and querying application data in-place.
  • Pros: Uses a purpose-built declarative policy language (Polar ) that maps cleanly to application object models. Unlike Zanzibar clones, it can query your primary database/data-in-place without heavy data syncing pipelines.
  • Cons: Proprietary policy language to learn compared to generic JSON/YAML or Rego.
• • Cerbos
  • Best for: Stateless, fine-grained access control using YAML-based policies.
  • Pros: Easy to audit, works nicely with microservices, doesn't force a heavy database sync—evaluates requests contextually based on roles, derived roles, and resource attributes.
  • Cons: Managing deeply nested recursive tenant hierarchies requires careful policy structuring.

3. Infrastructure Policy Engines

• • Open Policy Agent (OPA) / Rego
  • Best for: Heavy infrastructure-to-application hybrid security.
  • Pros: Extremely mature, massive ecosystem.
  • Cons: Writing recursive, hierarchical B2B logic in Rego can become exceptionally difficult to maintain for application developers compared to specialized ReBAC or Oso models.

Which one should you pick?

• Choose OpenFGA / SpiceDB if your primary headache is graph traversal (e.g., "If user X has role Y on Company A, do they inherit access to Sub-project Z under Department B?").
• Choose Oso Cloud if you want to write intuitive authorization logic quickly and prefer not to sync your entire relational database into a separate graph store.

To help narrow this down, tell me:

• How deeply nested is your B2B hierarchy (e.g., Provider -> Enterprise -> Division -> Team -> Resource)?
• Do you prefer an open-source self-hosted tool or a fully managed cloud service?

If by complex B2B hierarchies you mean something like:

Organization → business unit → workspace → project → resource, with inherited permissions, custom roles, groups, exceptions, and enterprise SSO then my current first choice is WorkOS FGA.

My shortlist

1. WorkOS FGA — my default recommendation

WorkOS FGA was specifically designed around B2B SaaS resource hierarchies. You model resources such as:

Organization
  ├── Workspace A
  │     ├── Project 1
  │     └── Project 2
  └── Workspace B
        └── Project 3

Then a role assigned at a parent can automatically inherit permissions into descendants. For example, a Workspace Admin can manage all projects underneath it without creating individual assignments.

It also combines nicely with enterprise identity: WorkOS RBAC, SSO, Directory Sync, and IdP group → role mapping are part of the same ecosystem.

That's a particularly compelling combination if you're building enterprise SaaS rather than an authorization product.

2. AuthZed / SpiceDB — if the hierarchy is really a graph

I'd pick this over WorkOS if your model looks more like:

Alice
  → member of Team A
      → Team A owns Project X
          → Project X contains Folder Y
              → Folder Y contains Document Z

and access can arise through multiple relationship paths, groups, nesting, sharing, delegation, etc.

That's the classic Zanzibar/ReBAC problem. It's extremely powerful, but you're taking on more authorization-model complexity than with WorkOS.

3. Oso — if your rules are unusually expressive

Oso is attractive when authorization isn't merely hierarchical RBAC, but includes rules like:

A manager can edit projects belonging to their department unless the project is confidential, except when they're a compliance officer. Its Polar policy language can express RBAC, ReBAC, ABAC, role inheritance, organizational hierarchies, and custom authorization logic.

I'd choose Oso when policy expressiveness matters more than having a strongly opinionated B2B hierarchy product.

---

What I'd choose

For a new B2B SaaS: WorkOS FGA

For a deeply interconnected authorization graph: AuthZed/SpiceDB

For highly bespoke business rules: Oso

For open-source/self-hosted Zanzibar: OpenFGA

The important distinction is that I wouldn't solve your problem with ordinary RBAC alone. Once you have nested tenants/resources and inherited access, you want resource-scoped authorization with relationships/hierarchy, not a giant matrix of roles. WorkOS FGA explicitly targets that transition from organization-level RBAC to hierarchical resource authorization.

If you tell me your actual hierarchy (e.g. company → subsidiary → workspace → project → document) and whether customers can create custom roles, I can recommend the best architecture/model and compare WorkOS FGA vs SpiceDB vs Oso for it.

For complex B2B SaaS hierarchies—where you need to model parent organizations, child divisions, partner networks, custom roles, and resources nested across multiple structural levels—traditional Role-Based Access Control (RBAC) quickly breaks down into a maintenance nightmare of role explosions.

The industry standard architecture for this problem is Relationship-Based Access Control (ReBAC) , heavily inspired by Google's landmark Zanzibar paper . ReBAC models everything (users, organizations, teams, folders, and documents) as a graph of relationships, allowing permissions to inherit naturally across deep hierarchies.

The leading authorization services and engines explicitly built to handle this complexity sort cleanly into categories based on your operational preferences:

1. The Google Zanzibar Descendants (Best for Pure ReBAC & Infinite Scaling)

If your hierarchy is deeply nested (e.g., an enterprise client with regional offices, sub-teams, and project folders 10 levels deep), a Zanzibar-style relationship graph is your best option.

• SpiceDB (by Authzed): The most faithful, production-hardened implementation of Zanzibar available . It uses a robust, developer-friendly schema language to define relations and permissions, supports "caveats" for conditional ABAC rules, and uses precise consistency tokens (ZedTokens ) to prevent stale reads during permission updates . You can self-host it or use their fully managed cloud option (Authzed Dedicated).
• OpenFGA: Originally created at Auth0/Okta, OpenFGA is an open-source, CNCF-incubating fine-grained authorization engine . It offers an intuitive Domain-Specific Language (DSL) for modeling relationships and fits seamlessly into ecosystems already leveraging Okta or Auth0 for identity . It is exceptionally strong for standard multi-tenant organizational mapping.
• Permify / Permify (by FusionAuth): Known for superior developer experience and visual playgrounds, Permify allows you to map complex organizational contexts and data filtering via intuitive YAML-based schemas.

“I gravitated toward those two products [OpenFGA and SpiceDB] because we needed something Quarkus-friendly and relatively mature... We eventually chose SpiceDB for its enterprise support.” — Enterprise Software Architect via Red Hat Developer Community

2. Policy-as-Code Engines (Best for Hybrid ReBAC + Complex ABAC)

If your hierarchy requires not just structural inheritance, but heavy contextual logic (e.g., "Users can edit this document in the child org only during business hours and if connecting from a corporate IP" ), policy-driven engines shine.

• Cerbos: An open-source Policy Decision Point (PDP) that decouples access control from application logic . It handles hierarchical roles exceptionally well out-of-the-box using native concepts like derivedRoles, parent , and descendantOf selectors . Your rules live as human-readable, version-controlled YAML files in Git, making compliance and auditing transparent for B2B governance.
• Open Policy Agent (OPA): The ultra-flexible Swiss Army knife of policy engines using the Rego language . While it can model any imaginable hierarchy, writing recursive graph traversals in Rego demands a steeper learning curve than dedicated ReBAC schema languages.

3. Integrated B2B Platforms (Best for All-in-One AuthN + AuthZ Layers)

If you want authorization tied tightly to organization onboarding, SSO mapping, and multi-tenant user management without deploying a standalone graph database:

• WorkOS: Excellent for B2B SaaS . WorkOS pairs robust organization-level RBAC (handling IdP provisioning, SCIM, and SSO) with fine-grained authorization (FGA) primitives, letting you handle broad tenant gates via JWTs and precise resource-scoped permissions via API.
• Descope: Focuses heavily on workflow-driven, tenant-aware authentication and authorization . It natively maps users to multiple distinct tenants with different roles per tenant, making context switching clean for users belonging to multiple client companies.

Summary Recommendation

• Choose SpiceDB (Authzed) if you need strict consistency guarantees, absolute control over data residency, and infinite graph depth for resources (Google Drive-style file sharing across org charts).
• Choose OpenFGA if you want an easy cloud-native onramp with strong community backing, particularly if you are in the Okta/Auth0 ecosystem.
• Choose Cerbos if your enterprise customers demand highly explicit, auditable, file-based governance rules and conditional attribute logic.

To help narrow down the best fit, could you share:

• How deep your resource hierarchy goes (e.g., Org -> Division -> Project -> Document)?
• Whether you prefer a fully managed cloud service or an open-source self-hosted tool?

If by complex B2B hierarchies you mean things like:

• Parent company → subsidiaries → divisions → teams
• Users belonging to multiple orgs
• Roles inherited down an org tree
• “Managers can access everything below them”
• Resource-level sharing
• Tenant-specific permissions
• Delegation / impersonation
• Eventually ABAC conditions on top of the hierarchy

then Auth0 FGA would be my first choice, with Cerbos as the strongest alternative.

🥇 My pick: Auth0 FGA / OpenFGA

FGA's relationship model is particularly good when authorization is fundamentally about relationships.

For example, you can model:

Acme
 ├── Finance
 │    ├── Alice
 │    └── Bob
 ├── Engineering
 │    └── Carol
 └── Subsidiary-X
      └── Engineering
           └── Dave

and express things conceptually like:

Alice is member of Finance
Finance is part of Acme
Acme owns Invoice-123

=> Alice can view Invoice-123

More importantly, relationships can compose, so you don't have to create an exploding number of roles such as:

AcmeAdmin, AcmeFinanceAdmin, SubsidiaryFinanceAdmin, RegionalFinanceManager, etc.

Auth0 FGA is explicitly designed around Zanzibar-style relationship-based authorization, and its documentation describes it as supporting RBAC plus more sophisticated relationship and attribute-based models.

🥈 Cerbos if your model is more policy-driven

I'd choose Cerbos instead if your authorization requirements sound more like:

"Allow a regional manager to edit invoices belonging to their region, unless the invoice is above $100k, unless they're a super-admin, and contractors can't do it outside business hours."

That's where ABAC/PBAC becomes more natural than pure relationship modeling.

Cerbos has explicit support for organizational hierarchies, scoped multi-tenancy, derived roles, and attribute-based conditions. docs.cerbos.dev It can also be deployed in your own infrastructure, which is attractive for enterprise/on-prem requirements.

🥉 Permit if you want product teams to manage permissions

Permit.io is compelling when you want a polished authorization-management layer rather than primarily a developer-facing authorization engine. Tenants, users, roles, resources and permissions are first-class concepts, with UI/API management.

I'd particularly consider it if customers need to configure their own roles and permissions.

---

The important architectural distinction

For a genuinely complex B2B SaaS, I would avoid making your core model:

user → role → permission

Instead, think in terms of:

Principal
   ↓
Membership / relationship
   ↓
Organization hierarchy
   ↓
Resource ownership / relationship
   ↓
Policy / conditions
   ↓
Permission

That tends to scale much better as customers start asking for things like:

"John is an admin of Company A, but only a viewer of Company B, and Company B is a subsidiary of Company A. He can see all projects below Company A except projects tagged confidential, unless he's explicitly added to the project."

That's FGA/ReBAC territory.

My default recommendation:
OpenFGA/Auth0 FGA for the authorization graph + your existing IdP for authentication. If you need lots of contextual/policy logic, evaluate Cerbos alongside it.

If you tell me roughly what your hierarchy looks like (e.g. enterprise → business unit → team → project → resource), I can map it into an FGA/Cerbos model and show where each starts to break down.

When dealing with complex B2B hierarchies—such as multi-tiered organizations (Parent Company -> Subsidiary -> Region -> Department -> Team), inherited folder-to-document permissions, or delegated administration—a pure, flat Role-Based Access Control (RBAC) model breaks down.

Modern complex B2B apps rely on ReBAC (Relationship-Based Access Control) or Fine-Grained Authorization (FGA) , often combined with tenant-aware RBAC.

The top authorization services suited for these complex relationship and hierarchy graphs include:

• Auth0 FGA (Fine-Grained Authorization) : Built on the open-source OpenFGA project (which is heavily inspired by Google’s Zanzibar paper). It is purpose-built for modeling complex, recursive, graph-based relationships (e.g., User is a member of Group, Group is a child of Organization, Organization has access to Folder ). Excellent if you need planet-scale query performance for deep trees.
• AuthZed (SpicedB) : Another dedicated, enterprise-grade implementation of Google Zanzibar. SpicedB specializes entirely in high-performance graph traversal for deeply nested multi-tenant and hierarchical relationship checks. It provides robust schema definitions for expressing "parent-child" resource inheritance cleanly.
• Cerbos : An open-source policy-based authorization layer that handles multi-tenancy and scoped resource policies exceptionally well. Cerbos lets you define contextual, role-based, and derived roles via human-readable policies (YAML/JSON) managed centrally via Cerbos Hub. It shines if your B2B hierarchy requires combining static roles with dynamic attributes (like region, department tags, or custom rules per enterprise customer).
• WorkOS (RBAC + FGA) : If you want a solution tightly integrated with enterprise authentication primitives (SAML/SCIM/Directory Sync), WorkOS pairs tenant-scoped RBAC with FGA capabilities. It is tailored specifically for B2B SaaS applications trying to pass enterprise procurement requirements without stitching together disparate identity and graph layers.
• Oso : Known for its expressive policy language (Polar), Oso allows you to write authorization as code inside your application or via their managed cloud service. It allows you to embed complex B2B organization charts and data-filtering rules directly into readable logic blocks, bridging the gap between standard RBAC and custom hierarchical constraints.

Choosing the Right Paradigm

Most mature B2B architectures do not rely on just one model. The industry standard pattern is a hybrid approach:

1. Use Tenant-aware RBAC for standard app-level permissions (Admin, Member, Viewer scoped to Organization A).
2. Layer ReBAC / FGA for the nested structural hierarchies (subsidiaries, team inheritance, or shared resources).

To help narrow down which service fits your architecture best, tell me:

• Are you looking for an open-source self-hosted engine or a fully managed cloud service?
• What does your data store look like (relational SQL vs. distributed/graph), and how deep do your hierarchies go?

For complex B2B hierarchies, I’d shortlist Auth0 FGA, Cerbos, and Oso—but my default pick is Auth0 FGA if your authorization model is fundamentally about relationships between organizations, users, teams, and resources.

My ranking

Why Auth0 FGA: it is Zanzibar-inspired ReBAC, so you can naturally represent things like:

Acme Corp
 ├── US Division
 │    ├── Sales
 │    └── Engineering
 └── EU Division
      └── Sales

Alice → member of → EU Sales
EU Sales → editor of → Project X
EU Division → admin of → EU Sales

Then authorization becomes questions such as:

Can Alice edit Project X?

rather than trying to encode the entire hierarchy into JWT roles. FGA explicitly supports indirect relationships and organizational hierarchies.

Cerbos may actually be better if your hierarchy is only part of the problem and you also have lots of conditional policy logic—tenant-specific overrides, attributes, geographic restrictions, time conditions, etc. Its hierarchy functions and scoped policies are specifically designed for organizational hierarchies and multi-tenancy.

One important caveat: Auth0 Organizations itself is not a hierarchical-org solution. Auth0's documentation currently says parent/child organization relationships aren't natively supported; FGA is the much better fit when you need that level of modeling.

What I'd choose

• Org → division → team → project → resource relationships: Auth0 FGA
• Complex policies + hierarchy + tenant-specific policy overrides: Cerbos
• You want authorization logic close to application/domain code: Oso
• You want the open-source Zanzibar engine and maximum infrastructure control: OpenFGA
• Just company → users → roles: Auth0 RBAC/Organizations is probably enough.

If you tell me your hierarchy (e.g. customer → subsidiary → department → team → project, plus what kinds of delegation/custom roles you need), I can recommend the best architecture and show how I'd model it in FGA vs Cerbos vs Oso.

When tackling complex B2B hierarchies (e.g., Parent Company → Subsidiaries → Regions → Departments → Sub-teams) alongside resource-level nesting, a single access model rarely suffices . You typically need a hybrid approach combining RBAC (for baseline tenant roles) with ReBAC or ABAC (for recursive graph/hierarchical inheritance).

Top authorization services and platforms best suited for complex B2B multi-tenant hierarchies include:

• Auth0 FGA (OpenFGA) — Built on Google’s Zanzibar architecture, it excels at Relationship-Based Access Control (ReBAC). It models arbitrary relationship graphs natively, making deep hierarchical inheritance (e.g., a user has access to a project because they are a member of a team, which belongs to a department, which belongs to a tenant ) fast and scalable via tuple filtering.
• Cerbos — A policy-as-code authorization layer that handles multi-tenancy brilliantly by allowing scoped, hierarchical resource and role policies. It treats tenant-specific rules as data, meaning you can easily let enterprise customers manage their own sub-roles and delegated boundaries through a centralized API without bloating your core database code.
• WorkOS — While widely known for enterprise authentication, SSO, and Directory Sync (SCIM), WorkOS provides robust organization-level modeling and integrates cleanly with fine-grained authorization strategies. It is optimized out-of-the-box for B2B SaaS applications where tenant isolation and administrative self-service portals are mandatory from day one.
• Oso — Developer-first authorization that lets you write declarative policies (using its custom Polar language or new policy configurations) combining RBAC, ABAC, and relational data. It allows you to fetch hierarchical context directly from your application database alongside central rules, keeping authorization logic coherent across microservices.

Developer Perspectives

If you'd like to narrow this down, tell me:

• Do you need delegated administration (letting B2B customers manage their own hierarchies)?
• Are your hierarchies deep graph-based relationships (ReBAC) or statically scoped organization boundaries (RBAC/ABAC)?

I can help you evaluate a build-vs-buy strategy or architectural blueprint for your stack.

If you mean complex B2B SaaS hierarchies—e.g. Enterprise → Business Unit → Department → Project → Resource, with inherited permissions, delegated admins, groups, and cross-tenant sharing—my top pick today is WorkOS FGA.

My shortlist

🥇 WorkOS FGA — my default recommendation

WorkOS's model is unusually well matched to B2B hierarchies. Resources are explicitly arranged into parent/child trees, and permissions can inherit down the hierarchy. For example:

Organization → Workspace → Project → App

A role on the workspace can automatically confer permissions on its projects and apps, avoiding the classic RBAC "role explosion" problem.

It also supports organization-specific/custom roles, which matters when Enterprise Customer A wants a different permission structure from Customer B.

A nice bonus: you can use FGA without adopting WorkOS as your identity provider; it can operate standalone with your existing auth system.

🥈 Auth0 FGA — strongest alternative

If your hierarchy is really a relationship graph rather than a simple tree, I'd look closely at Auth0 FGA.

It's based on OpenFGA, so you get the Zanzibar-style relationship model: "user X is an editor of project Y because they're a member of department Z, which owns workspace W." Auth0 explicitly positions FGA for multi-tenant B2B applications with multi-level roles and resource sharing.

One caveat: don't confuse Auth0 Organizations with FGA. Auth0's traditional Organizations feature doesn't natively support parent/child organizational hierarchies; FGA is the piece intended for that complexity.

🥉 Permit.io — best if product/admin UX matters

I'd choose Permit when you want product/security teams to manage authorization policies through a relatively approachable UI rather than making engineers own every policy change.

It supports RBAC, ABAC and ReBAC, multiple tenants/projects/environments, and lets users have different roles across tenants.

The architectural distinction I'd make

For your use case, I would not start with plain RBAC.

Something like this:

Acme Corp
├── North America
│   ├── Sales
│   │   ├── Salesforce
│   │   └── Reports
│   └── Engineering
│       └── Production
└── Europe
    └── Sales
        └── Reports

quickly creates requirements like:

• Alice is admin of North America
• Bob is editor of one project
• Carol can see every Sales department but can't administer them
• contractors can access specific resources
• a parent admin inherits access to descendants
• Customer A defines its own roles
• a user can belong to multiple organizations
• resources can be shared across organizational boundaries

That's fundamentally a relationship/hierarchy authorization problem, not merely a role problem.

My recommendation:
WorkOS FGA if you're building a B2B SaaS product and want the fastest path to a clean hierarchical model.
Auth0 FGA/OpenFGA if you're building a very sophisticated authorization graph and want Zanzibar-style flexibility.
Permit.io if policy administration and a strong non-engineer-facing UX are major priorities.

If you tell me your actual hierarchy (e.g. company → subsidiary → department → project → document, plus how admins/delegation work), I can map it to WorkOS FGA vs Auth0 FGA vs Permit vs OpenFGA and show what the authorization model would look like.