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FoxyInvoice keeps multiple companies in one running system and database, then scopes access by tenant identity. Its described safeguards combine tenant-aware authentication, automatic read filters, write-time tenant stamping, server-side permissions and cross-tenant integration tests. These are the chapter author’s account of one production system—not an independent audit or a universal guarantee.
What multi-tenancy means in FoxyInvoice
FoxyInvoice uses a shared application and database for multiple companies. The intended boundary is that each company can access only its own records. In this design, a missed tenant condition in a query is a realistic application bug: as chapter author Lith SEO puts it, “The realistic threat is your own future self at 2 a.m. writing a query that forgets the tenant filter.”
The system’s approach layers safeguards rather than relying on a single check. Tenant identity enters with authentication, constrains database reads, is stamped onto new records, and is exercised in integration tests.
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Users can sign in with email and password, with Argon2id used for password hashing, or through Google SSO. After successful login, FoxyInvoice issues a short-lived JSON Web Token (JWT) containing the user ID, tenant ID and permission claims, along with a rotating refresh token. The browser sends the JWT with API calls, and the server verifies its signature.
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The tenant ID in the verified request context provides the scope used by the data-access safeguards. A tenant identifier supplied by the browser is not supposed to let a caller select a different workspace when creating a record; the described save interceptor assigns the caller’s tenant instead.
How the database separates tenant data
Reads: EF Core global query filters
FoxyInvoice uses Entity Framework Core (EF Core) global query filters to constrain queries for tenant-scoped entities to the active tenant. The intent is to make tenant scoping automatic for ordinary entity queries, reducing the chance that each developer must remember to add the condition manually.
The chapter also describes a per-tenant model-cache key. That matters because EF Core caches models: when requests from different tenants interleave, the cached filter configuration must still correspond to the active tenant rather than accidentally retaining another tenant’s scope.
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A save interceptor stamps new rows with the caller’s tenant. Under the described behavior, a submitted tenant ID does not determine which workspace owns the new record. This complements read filters: restricting which rows can be queried does not by itself prevent a write from being assigned to the wrong tenant.
Exceptions: queries that bypass filters
Some background jobs use IgnoreQueryFilters(), which bypasses the global filters. Those jobs must handle tenant scope explicitly. This is a deliberate escape hatch, not a safe default: reviewers should verify how each such job selects tenants and records, and whether its scope is limited to the work it is meant to perform.
How the tenant boundary is tested
The chapter describes integration tests that sign in as two tenants, create overlapping data, and check that neither tenant can see the other’s records. It says these tests run in continuous integration on every push. Testing both tenants against overlapping data is useful because it exercises the boundary under conditions where the same kinds of records exist in each workspace.
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These tests provide repeatable evidence for the behavior they cover; they do not establish that every query path, background job, configuration or production deployment is correct. The chapter does not provide independent test artifacts or an external assessment.
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How permissions and document sharing differ
Role permissions
Role-based access control maps roles to permission strings. The decisive check is the server-side HasPermission check. Route guards and hidden interface elements can improve the user experience, but they are presentation aids: hiding an action in the UI is not a substitute for rejecting an unauthorized API request.
Share links
A separate sharing mechanism uses an unguessable 32-byte URL token scoped to one document. The chapter says these links expire and can be revoked. Because a share URL is a bearer credential, its document scope, expiration and revocation are important limits on what possession of the link permits.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Operational safeguards beyond tenant filtering
Isolation controls sit alongside operational practices that address other ways business data or credentials could be exposed or lost. The chapter reports that FoxyInvoice:
- Records before-and-after JSON snapshots for audit activity.
- Runs nightly
pg_dumpbackups, gzip-compresses them, checks their size and copies them off-host. - Stores payment-method identifiers while Stripe holds the payment methods themselves.
- Provides an export workflow.
- Disables users immediately and hard-deletes their data after a 30-day grace period.
- Uses a gitleaks gate to check the repository for secrets.
These practices complement tenant scoping; they do not replace it. The chapter describes the procedures but does not establish independent validation of their operation or recovery outcomes.
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This is a first-person description of FoxyInvoice’s controls, not an independent audit, penetration test or certification. It does not prove that every control is implemented correctly or that no cross-tenant exposure is possible. The author also notes that security work remains to mature, including deeper account-takeover hardening and broader defense in depth.
For developers, the key design lesson is the combination: establish tenant context from verified identity, scope routine reads automatically, stamp tenant ownership on writes, scrutinize filter bypasses, enforce permissions on the server, and test that separate tenants cannot see one another’s data.
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