Best authorization service for complex B2B hierarchies?

For complex B2B hierarchies, I’d look primarily at relationship-based / fine-grained authorization (ReBAC/FGA) rather than a traditional RBAC-only service.

Shortlist

Service	Particularly good for	Hierarchies	My take
WorkOS FGA	B2B SaaS with org → workspace → project → resource structures	Native hierarchical inheritance	Very strong fit
Auth0 FGA	Complex ReBAC at large scale, especially if already using Auth0	Yes	Strong choice for sophisticated authorization
Permit.io	Teams wanting policy management/UI plus RBAC/ABAC/FGA-style capabilities	Strong multi-tenancy	Good if policy administration is important
Oso	Developers wanting authorization logic close to application code	Flexible	Good developer-centric option
OpenFGA	Maximum control / open-source Zanzibar model	Excellent	Best if you're willing to own more infrastructure

Why I'd look at WorkOS FGA first

For a hierarchy like:

Organization
 ├── Division
 │    ├── Workspace
 │    │    ├── Project
 │    │    └── Project
 │    └── Workspace
 └── Division

WorkOS FGA explicitly models resources as a hierarchy and lets roles assigned higher in the tree inherit permissions downward. For example, a workspace admin can automatically receive permissions on its projects and apps, while a project editor can be limited to one project.WorkOS+1

It also supports discovering which resources a user can access and who has access to a resource, which matters a lot for B2B UIs rather than merely answering can(user, action, resource).WorkOS

One important constraint: WorkOS FGA currently models a single-parent hierarchy, with a maximum depth of five levels. That's worth checking against your domain if resources can belong to multiple organizational branches.WorkOS

When I'd choose something else

• Auth0 FGA — if you're already deeply invested in Auth0 or want a very general Zanzibar-style ReBAC system. Auth0 describes FGA as relationship-based authorization designed for multi-tenant B2B APIs and very large resource graphs.Auth0
• Permit.io — if you want authorization policy administration to be a major product surface. Its model has first-class tenants and supports multi-tenant authorization.Permit.io Docs
• OpenFGA — if avoiding vendor lock-in and having direct control over the authorization engine is more important than getting a turnkey SaaS experience.
• Oso — if your authorization rules are highly application-specific and your team prefers implementing the policy model in code rather than maintaining a centralized authorization service.

The biggest architectural question is whether your hierarchy is actually a tree or a graph. If you have things like user → team → subsidiary → organization, cross-org resource sharing, delegated administration, exceptions/denials, and multiple parents, I'd lean toward a Zanzibar/OpenFGA-style graph model rather than a conventional RBAC product.

If you tell me your hierarchy (e.g. customer → business unit → site → project → document, plus how roles/inheritance work), I can compare WorkOS FGA vs Auth0 FGA vs OpenFGA vs Permit vs Oso specifically for that model.

Organization
 ├── Division
 │    ├── Workspace
 │    │    ├── Project
 │    │    └── Project
 │    └── Workspace
 └── Division

WorkOS FGA explicitly models resources as a hierarchy and lets roles assigned higher in the tree inherit permissions downward. For example, a workspace admin can automatically receive permissions on its projects and apps, while a project editor can be limited to one project.workos.com+1

It also supports discovering which resources a user can access and who has access to a resource, which matters a lot for B2B UIs rather than merely answering can(user, action, resource).

For complex B2B hierarchies (e.g., Parent Company → Subsidiary → Regional Division → Team, with inherited roles, cross-organization sharing, and resource-level overrides), traditional flat Role-Based Access Control (RBAC) falls short.checkthat.ai

The industry standard for this exact problem is Relationship-Based Access Control (ReBAC) , heavily inspired by Google's Zanzibar architecture, or specialized B2B identity platforms that treat multi-tenancy and hierarchies as first-class citizens.pkgpulse.com+2

Top Dedicated ReBAC Engines (Best for Deep, Arbitrary Graph Hierarchies)

If your hierarchy is deeply nested, highly dynamic, or requires defining graph relationships (e.g., "User is an editor of Folder, which belongs to Organization, which is a subsidiary of Enterprise" ), you want a dedicated fine-grained authorization (FGA) service:

1. OpenFGA (Apache 2.0)
   • Best for: Most modern engineering teams looking for a balance of flexibility, strong ecosystem backing (originally created by Auth0/Okta), and great SDK support.
   • Why it fits: Uses a clean, intuitive DSL to model relationship tuples. It excels at computing recursive hierarchy checks (allowed if user is member of parent group ) at scale with low latency.authzed.com+1
2. SpiceDB by AuthZed (Apache 2.0)
   • Best for: Enterprise-grade, "Zanzibar-purist" architectures requiring strong consistency guarantees and massive scale (used by companies like OpenAI for ChatGPT Enterprise).
   • Why it fits: Extremely faithful to the Google Zanzibar paper, offering robust watch/cache invalidation APIs and bulletproof handling of massive, deep relationship graphs.sph.sh+2
3. Permify (AGPL v3)
   • Best for: Rapid development and teams wanting a visual playground with native data-filtering capabilities to map permissions directly to database queries.
   • Why it fits: Very developer-friendly schema declarations (YAML-based) and great tooling for visualizing complex tenant trees out of the box. (Note the AGPL license if you distribute the core engine internally/commercially).pkgpulse.com+1

Top B2B SaaS Platforms (Best for Hierarchies + Out-of-the-Box UI/Admin Portals)

If you don't just want a raw permission evaluation engine, but also need the UI components, tenant management, SCIM provisioning, and delegated admin panels for those hierarchies:

1. Frontegg
   • Best for: B2B SaaS products needing hierarchical multi-tenancy and self-service admin portals without building them from scratch.
   • Why it fits: Uniquely handles nested/hierarchical tenant structures natively (e.g., managing sub-organizations and inherited roles across tiers) right out of the box, whereas other auth providers require heavy custom logic.checkthat.ai
2. PropelAuth
   • Best for: B2B-first architectures where organizations and multi-level structuring are core to the application from day one.
   • Why it fits: Avoids the trap of retrofitting a consumer auth tool into a B2B app, cleanly managing organizational boundaries and role mappings.propelauth.com

Policy-as-Code Alternative (Best for Complex Attribute Logic)

• Cerbos : If your hierarchy rules depend heavily on context and attributes (ABAC)—such as "Can edit only if the document is in the same region and the user's shift is active" —Cerbos lets you write human-readable YAML policies for roles and resource attributes without dropping down into a pure graph tuple store.startwithidentity.com

To help narrow down the ideal fit, tell me:

• Do you need an infrastructure service (just the permission-check API like OpenFGA) or an all-in-one B2B user management platform (handling logins, UI, and tenant admin)?
• How deep does the hierarchy go (e.g., 2 levels vs. arbitrary nesting)?

For complex B2B hierarchies—e.g. customer → business unit → team → project, delegated admins, inherited permissions, cross-org relationships, and tenant-specific roles—I’d shortlist SpiceDB/AuthZed, OpenFGA, Cerbos, and Oso.

The key distinction is whether your authorization model is primarily a relationship graph (ReBAC) or a policy/rules engine (ABAC/RBAC/PBAC).

My practical take

If your hierarchy looks like a graph, start with SpiceDB/AuthZed. Its core abstraction is relationships: you define relationships between subjects and resources and ask questions such as whether a subject can perform an action on a resource. That's particularly natural for B2B structures such as:

Acme
├── Europe
│   ├── Germany
│   │   ├── Sales
│   │   └── Support
│   └── France
└── US
    └── Sales

You can express things like:

alice is member of germany_sales
germany_sales is member of europe
europe has viewer access to report_123

and derive effective permissions through the graph. SpiceDB is explicitly designed around this Zanzibar-style model and can operate as a centralized authorization service.GitHub

OpenFGA is the other strong choice if you want the same general Zanzibar/ReBAC approach. I'd particularly consider it when you want an open-source, relationship-oriented model and don't need a heavily policy-centric authorization system.

Cerbos becomes particularly interesting when your requirements include lots of conditional policy logic in addition to hierarchy. Its current documentation explicitly supports organizational hierarchies, multi-tenancy, scoped policies, tenant-specific roles, and hierarchy functions such as ancestorOf, descendentOf, and overlaps.Cerbos+1

For example, Cerbos can handle rules along the lines of:

Regional admins can approve expenses for descendants of their region, unless the expense exceeds $50k, in which case a global finance role is required. That's more naturally expressed as a policy engine than as a pure relationship graph.

What I'd choose based on your architecture

• "Who can access what through a complicated org/resource graph?" → SpiceDB/AuthZed
• "We want Zanzibar/ReBAC and an open-source ecosystem" → OpenFGA
• "Permissions depend on hierarchy + attributes + conditions + tenant-specific policies" → Cerbos
• "Authorization logic should feel close to application/domain code" → Oso

One particularly important question is whether you need permission inheritance versus merely tenant isolation. For example, if a user at Acme/EU automatically gets access to every descendant office, while a user at Acme/Germany gets only Germany resources, that's a strong ReBAC use case. If you instead have hundreds of conditional business rules, Cerbos becomes more compelling.

If you tell me your hierarchy (e.g. org → subsidiary → department → team → project, plus how users can belong to multiple orgs), I can map it to SpiceDB vs OpenFGA vs Cerbos and show the actual authorization schema for each.

Acme
├── Europe
│   ├── Germany
│   │   ├── Sales
│   │   └── Support
│   └── France
└── US
    └── Sales

You can express things like:

alice is member of germany_sales
germany_sales is member of europe
europe has viewer access to report_123

and derive effective permissions through the graph. SpiceDB is explicitly designed around this Zanzibar-style model and can operate as a centralized authorization service.github.com

OpenFGA is the other strong choice if you want the same general Zanzibar/ReBAC approach. I'd particularly consider it when you want an open-source, relationship-oriented model and don't need a heavily policy-centric authorization system.

Cerbos becomes particularly interesting when your requirements include lots of conditional policy logic in addition to hierarchy. Its current documentation explicitly supports organizational hierarchies, multi-tenancy, scoped policies, tenant-specific roles, and hierarchy functions such as ancestorOf, descendentOf, and overlaps.

For example, Cerbos can handle rules along the lines of:

Regional admins can approve expenses for descendants of their region, unless the expense exceeds $50k, in which case a global finance role is required. That's more naturally expressed as a policy engine than as a pure relationship graph.

If by “complex B2B hierarchies” you mean things like:

Enterprise → divisions → departments → teams → projects, with inherited permissions, delegated admins, custom roles, and exceptions

then I’d shortlist these:

Service	Best for	Hierarchies	ReBAC/FGA	ABAC	My take
WorkOS FGA	B2B SaaS with org/workspace/project trees	⭐⭐⭐⭐⭐	⭐⭐⭐⭐⭐	—	Best default
Auth0 FGA	Complex authorization + Auth0 identity stack	⭐⭐⭐⭐⭐	⭐⭐⭐⭐⭐	Limited/adjacent	Best if using Auth0
Permit.io	Flexible authorization with strong UI	⭐⭐⭐⭐⭐	⭐⭐⭐⭐⭐	⭐⭐⭐⭐	Best developer experience
Cerbos	Highly custom policy/ABAC requirements	⭐⭐⭐⭐⭐	⭐⭐⭐	⭐⭐⭐⭐⭐	Best policy engine
Oso	Developer-controlled authorization logic	⭐⭐⭐⭐	⭐⭐⭐⭐⭐	⭐⭐⭐⭐	Strong if you want code-centric control

🥇 My pick: WorkOS FGA

For a modern B2B SaaS product, WorkOS FGA is probably where I'd start. Its resource model explicitly supports hierarchical resources—organizations, workspaces, projects, etc.—with permissions inherited down the hierarchy. Roles can be scoped to individual resources rather than merely to an entire tenant.workos.com

That maps very naturally to something like:

Acme Corp
├── North America
│   ├── Sales
│   │   ├── Project A
│   │   └── Project B
│   └── Engineering
└── Europe
    └── Sales

You can express things like:

• Alice is admin of Acme
• Bob is admin of North America
• Carol is manager of Sales
• Dave can edit Project A
• permissions inherited from parent resources
• custom roles at different hierarchy levels

WorkOS also positions FGA as an extension of its existing RBAC/SSO/Directory Sync stack, which is particularly attractive if you're already using WorkOS for B2B identity.workos.com

🥈 Auth0 FGA

If you're already heavily invested in Auth0, I'd seriously consider its FGA product. It's relationship-based and designed specifically for multi-tenant B2B authorization with complex resource relationships. It's built on OpenFGA, giving you a Zanzibar-style authorization model.auth0.com

One important distinction: Auth0 Organizations themselves don't natively support parent/child organization hierarchies. Auth0's own documentation currently recommends modeling such relationships externally when needed.workos.com+3

So I'd choose Auth0 FGA rather than trying to force Auth0 Organizations/RBAC to represent a deep hierarchy.

🥉 Cerbos

I'd choose Cerbos if your problem is less “model my SaaS resource graph” and more:

“We have extremely complicated policy decisions involving user attributes, resource attributes, organizational scope, geography, time, compliance, etc.”

Cerbos supports ABAC/PBAC and explicit hierarchy functions such as ancestorOf, descendentOf, and immediateParentOf.www.cerbos.dev

For example:

Allow if:
  user.role == "regional_manager"
  AND user.region is ancestor of resource.region
  AND resource.classification <= user.clearance
  AND request.environment == "corporate"

That's where Cerbos starts becoming more compelling than a pure FGA system.

Permit.io

Permit.io is particularly interesting if you want a more managed, visual authorization experience. Its ReBAC implementation is explicitly designed around graph relationships and hierarchical structures.docs.permit.io

I'd look at it if you want product/security teams to have substantial ability to inspect and manage authorization policies without everything living in application code.

What I'd choose by architecture

Typical B2B SaaS:

WorkOS FGA

Already using Auth0:

Auth0 FGA / OpenFGA

Lots of contextual policy logic:

Cerbos

Want a highly visual/managed authorization platform:

Permit.io

Want maximum developer/code-level control:

Oso

The key architectural decision isn't really RBAC vs. RBAC. For deep B2B hierarchies, I'd strongly favor ReBAC/FGA as the underlying model, with RBAC layered on top. A pure RBAC system tends to explode into role variants once you introduce nested organizations, resource-specific permissions, delegated administration, and customer-specific exceptions.

If you tell me your hierarchy (e.g. company → subsidiaries → teams → projects → resources) and whether you're already using Auth0, WorkOS, Okta, or another IdP, I can narrow this to a specific recommendation and architecture.

When handling complex B2B hierarchies (e.g., multi-layered organizations, parent-child tenant accounts, granular resource sharing across departments, and custom enterprise roles), standard Role-Based Access Control (RBAC) quickly breaks down.osohq.com+1

The industry standard for modeling nested hierarchies is Relationship-Based Access Control (ReBAC) —popularized by Google Zanzibar—often paired with policy-as-code.startwithidentity.com+1

The top authorization services and engines suited for complex B2B scenarios are broken down below by their strengths.

Top Solutions for Complex B2B Hierarchies

1. • OpenFGA (Open Source / Managed by Okta/Auth0)
   • Best for: Pure Zanzibar-style graph relationships.
   • Why it fits: Modeled explicitly around tuples (user, relation, object ), making it trivial to say "User X is an admin of Organization A, which is a parent of Business Unit B, which owns Document C." Highly scalable and built for massive graph traversals.
2. • SpiceDB / AuthZed (Open Source / Managed SaaS)
   • Best for: Enterprise-grade Google Zanzibar implementation with a robust schema language.
   • Why it fits: SpiceDB allows you to write explicit schema definitions for your B2B org chart. If you need absolute consistency, strong typing for relationships, and an engine that handles deep hierarchical nesting without breaking a sweat, this is a top contender.
3. • Cerbos (Open Source / Managed Control Plane)
   • Best for: Policy-as-code with intuitive YAML definitions.
   • Why it fits: Unlike pure ReBAC graph databases, Cerbos combines RBAC, ABAC, and role hierarchies into clean, human-readable policy files. It works exceptionally well if your B2B hierarchy involves complex conditions (e.g., "Can view only if user is in the same geographic region and has the manager role" ). It can run locally as a high-performance sidecar/WASM.medium.com+2
4. • Permit.io (Managed Orchestration Platform)
   • Best for: Fast implementation with a unified UI for non-technical stakeholders.
   • Why it fits: Permit acts as an orchestration layer on top of engines like OPA or OpenFGA. If your B2B product needs an administrative dashboard where customers can define their own sub-roles and permissions within their organizational hierarchy, Permit provides the UI out-of-the-box.checkthat.ai+2
5. • Oso Cloud (Managed Service)
   • Best for: Developer-first frameworks tailored specifically for B2B SaaS authorization.
   • Why it fits: Oso built their declarative language (Polar) specifically to solve multi-tenancy, data-filtering (fetching a list of records a user is authorized to see in a SQL database), and role/hierarchical nesting inside B2B applications.

Which one should you pick?

• Go with OpenFGA or SpiceDB if your hierarchy is deeply nested, graph-heavy, and you want a proven Google Zanzibar architecture.
• Go with Cerbos if you prefer managing file-based policies and need a mix of roles, attributes, and regional conditions.
• Go with Permit.io or Oso if you want fast developer velocity, robust SDKs, and built-in tooling that maps directly to B2B multi-tenant data models.checkthat.ai+2

To help narrow down the ideal choice, tell me:

• Are you looking for a fully managed cloud service or a self-hosted open-source tool?
• Do your enterprise customers need a custom UI to configure their own sub-roles within your app?

For complex B2B hierarchies (multi-tenant SaaS, organizations → departments → teams → projects → resources, delegated admins, inherited permissions, customer-specific roles), the best choices are usually fine-grained authorization (FGA) systems, especially relationship-based access control (ReBAC) rather than traditional RBAC.Chaos and Order+1

My shortlist:

Service	Best fit	Why
Auth0 Fine-Grained Authorization (FGA)	Most B2B SaaS teams wanting managed infrastructure	Zanzibar-style ReBAC, strong fit for org hierarchies and resource sharing, managed service based on OpenFGA.Auth0+1
OpenFGA	Teams wanting open source and control	Zanzibar-inspired model, good for modeling nested organizations, groups, roles, and inheritance.Deepak Gupta+1
AuthZed SpiceDB	Large-scale authorization graphs	Very mature Zanzibar-style implementation; good when permissions are deeply relational.Start with Identity
Amazon Web Services Cedar / Amazon Verified Permissions	AWS-heavy environments with policy-driven access	Strong for attribute/context rules and policy auditing, less natural for deeply nested resource graphs.Chaos and Order
Oso	App-level authorization with custom logic	Good hybrid of RBAC/ABAC/ReBAC, especially when authorization is tightly coupled to application behavior.Bersyn

My recommendation by architecture

Choose Auth0 FGA / OpenFGA if your model looks like:

Customer A
 └── Division
      └── Team
           └── Project
                └── Document

User → Team member
Team → Project access
Project → Document inheritance

Examples:

• "A manager can edit everything in their department."
• "A customer admin can invite users only inside their tenant."
• "A user can access a document because they belong to a group that has access."
• "Partners can access selected customer resources."

This is exactly the problem ReBAC systems were designed for.Auth0 FGA Docs

Choose Cedar / OPA-style policy engines if your rules are more like:

• "Allow access only during business hours."
• "Contractors cannot download data."
• "Users in region EU need GDPR restrictions."
• "Allow if risk score < threshold."

Those are attribute/context decisions rather than relationship graphs.OpenFGA

A practical B2B SaaS stack I would consider

For a new enterprise SaaS:

• Identity: your IdP (Okta, Auth0, Azure AD, etc.)
• Authorization graph: OpenFGA or Auth0 FGA
• Policy exceptions: Cedar or OPA for unusual rules
• Application database: stores business data, not permission logic

Avoid putting thousands of roles like:

Customer_Admin_EU_ReadOnly
Customer_Admin_US_ReadWrite
Partner_Manager_ProjectA
Partner_Manager_ProjectB

That becomes a "role explosion" problem. A relationship model handles this more naturally.Chaos and Order

If I had to pick one

• Startup / SaaS building a complex multi-tenant product: Auth0 FGA or OpenFGA
• Enterprise platform team with infrastructure expertise: SpiceDB
• AWS-first company with mostly attribute rules: Cedar
• Simple RBAC only: don't buy an FGA system; use your framework/database roles

For most modern B2B SaaS products with customer hierarchies, I would start with OpenFGA (or managed Auth0 FGA) because it maps closely to how customers actually think about ownership, membership, delegation, and inheritance.Auth0+1

If you describe your hierarchy (e.g., tenant → org → workspace → project → object, plus your admin/delegation rules), I can suggest a concrete authorization model.

For complex B2B hierarchies (multi-tenant SaaS, organizations → teams → projects → resources, delegated admins, inherited permissions, external collaborators), the best authorization services are usually fine-grained authorization (FGA) systems rather than traditional RBAC products. They model relationships like “user is a member of org,” “team owns project,” or “customer admin can manage users in their tenant.”Auth0 FGA Docs+1

My shortlist:

Service	Best fit	Strengths	Trade-offs
Auth0 FGA	Most B2B SaaS teams wanting managed infrastructure	Zanzibar-style relationship model, hosted, strong tooling, good for complex hierarchies	Vendor-managed; less control than self-hostingAuth0 FGA Docs+1
OpenFGA	Teams wanting open source and portability	Mature Zanzibar-inspired model, self-hostable, flexible schemas	You operate scaling, storage, availability, upgradesAuth0 Developer Center+1
AuthZed	Large-scale authorization infrastructure	Very Zanzibar-oriented, strong developer tooling, good for complex graphs	Requires deeper authorization modeling expertisepkgpulse
Oso	Teams wanting policy-as-code	Developer-friendly, good embedded authorization patterns	Less ideal if your main problem is massive relationship graphs
Permit.io	Teams wanting UI-driven policy management	Faster adoption, product teams can manage policies	May be less suited for extremely graph-heavy models

What I’d choose by architecture

1. B2B SaaS with tenants, sub-tenants, and resource sharing

Pick Auth0 FGA or OpenFGA.

Example model:

Acme Corp
 ├── Engineering Team
 │    ├── Project A
 │    └── Project B
 └── Finance Team

Alice:
- member of Engineering
- admin of Project A
- viewer of Project B

A relationship model handles this naturally:

alice -> member -> engineering-team
engineering-team -> can_edit -> project-a

This avoids creating hundreds of roles like:

EngineeringProjectAAdmin
EngineeringProjectBViewer
FinanceProjectOwner
...

which is where RBAC tends to collapse.Deepak Gupta

2. Enterprise customers with delegated administration

Look for:

• nested groups
• inheritance
• permission checks at object level
• auditability
• “why was access granted?” explanations

FGA-style systems are strong here.Auth0 FGA Docs

3. Highly regulated / self-hosted environments

Choose:

• OpenFGA
• SpiceDB

You keep authorization data inside your infrastructure.

4. Simple SaaS roles only

Do not add FGA complexity if you only have:

Admin
Manager
User
Viewer

A normal RBAC layer may be enough.

My default recommendation

For a new B2B SaaS product in 2026:

1. Start with OpenFGA if you have strong engineering ownership and want control.
2. Use Auth0 FGA if you want managed operations and faster production readiness.
3. Consider SpiceDB if authorization itself is a core platform capability and you expect very complex permission graphs.

A good architecture is often:

Identity provider (authentication)
          |
          v
Authorization service (FGA)
          |
          v
Application APIs

Keep authentication (who the user is) separate from authorization (what they can do).Auth0 Developer Center

If you share your hierarchy shape (e.g., customer → account → workspace → project → document, plus whether users can belong to multiple customers), I can suggest the best model and vendor fit.

4. Simple SaaS roles only

Do not add FGA complexity if you only have:

Admin
Manager
User
Viewer

A normal RBAC layer may be enough.

My default recommendation

For a new B2B SaaS product in 2026:

For complex B2B hierarchies (e.g., multi-level organizations, parent-child tenant structures, team-within-department nesting, and delegated administration), traditional flat RBAC breaks down. You need a dedicated Fine-Grained Authorization (FGA) or Relationship-Based Access Control (ReBAC) service.youtube.com+3

The top authorization services for complex B2B hierarchies are categorized below by their architectural strengths.

1. Google Zanzibar-Style ReBAC (Best for Deep, Graph-Based Hierarchies)

If your B2B hierarchy involves resources inheriting permissions down arbitrary tree structures (e.g., User -> Member of Team -> Part of Department -> Owned by Tenant Corp ), a ReBAC model inspired by Google Zanzibar is the gold standard.identigy.com+1

• • OpenFGA (Open Source / Managed by Auth0/Okta): Highly popular, developer-friendly DSL (Domain Specific Language), and purpose-built for modeling complex relationships and contextual tuples. Excellent if you want an open-source core with enterprise backing.sph.sh+3
• • SpiceDB by Authzed (Open Source / Managed Cloud): Built specifically to replicate Google Zanzibar at scale. It handles massive graph traversals effortlessly and treats everything—including hierarchical group membership and resource ownership—as a relationship.sph.sh+2

2. Policy-as-Code (Best for Context-Heavy, Dynamic B2B Rules)

If your hierarchies are relatively straightforward, but your access logic relies heavily on contextual attributes (e.g., can this user edit this resource only if the organization's subscription tier is Enterprise and it's during business hours? ), Policy-as-Code engines shine.

• • Cerbos (Open Source / Managed Cloud): Uses human-readable YAML policies and CEL (Common Expression Language). It natively handles multi-tenant B2B scoping and provides a powerful "query plan" feature that translates authorization rules directly into database filters (crucial for listing only the resources a user is allowed to see in a massive enterprise tree).cerbos.dev+2
• • Open Policy Agent (OPA) / Rego : Extremely powerful and battle-tested in cloud-native environments, though writing complex recursive hierarchy logic in Rego has a steeper learning curve than dedicated ReBAC DSLs.

3. Integrated Auth + Authorization (Best for All-in-One B2B SaaS)

If you do not want to decouple authentication and authorization into two entirely different vendors and prefer an integrated approach that understands "Organizations" out of the box:

• • Auth0 FGA / Auth0 Organizations : Combines enterprise-grade multi-tenant identity features with fine-grained relationship modeling. Ideal if you are already using or leaning into the Auth0 ecosystem for SSO/Directory Sync and want native hierarchy mapping.auth0.com+1
• • WorkOS : While primarily an enterprise authentication and directory sync leader, WorkOS pairs exceptionally well with external FGA engines if you need robust B2B primitives (SCIM, SAML, Admin Portals) alongside your hierarchy management.propelauth.com+1

Which one should you pick?

• Choose SpiceDB or OpenFGA if your hierarchy is deeply nested (e.g., folders inside folders inside organizations, with users having varying roles at each node).auth0.com+2
• Choose Cerbos if you want fast implementation, human-auditable policy files, and need the engine to help generate database queries for paginated/filtered list views.cerbos.dev+1

To help narrow down the ideal choice, tell me:

• Are your hierarchies arbitrarily deep (nested groups/folders) or strictly two-level (Tenant -> Users)?
• Do you prefer an open-source stack to self-host or a fully managed cloud service?