docs(security): document single-tenant deployment model (#169)

README.md

@@ -153,7 +153,7 @@ Running in **HTTP mode** — OAuth2, CORS, and the `HTTP_SECURITY_ENABLED` toggl
 **Using it**
 - [Quick start](docs/site/content/pages/mcp/quick-start.md) · [Client setup](docs/site/content/pages/mcp/clients/) — Claude Desktop, Claude Code, VS Code, Cursor, JetBrains, MCP Inspector
 - [Observability](docs/site/content/pages/mcp/observability.md) — OpenTelemetry traces, metrics, logs
-- Security: [STDIO model](docs/security/stdio.md) · [HTTP model](docs/security/http.md) · OAuth2 setup: [Auth0](docs/security/auth0.md) · [Keycloak](docs/security/keycloak.md)
+- Security: [Deployment model (single-tenant)](docs/security/deployment-model.md) · [STDIO model](docs/security/stdio.md) · [HTTP model](docs/security/http.md) · OAuth2 setup: [Auth0](docs/security/auth0.md) · [Keycloak](docs/security/keycloak.md)
 
 **Developing it**
 - [Development guide](dev-docs/DEVELOPMENT.md) — build, run, test, IDE, native image, SBOM · [Architecture](dev-docs/ARCHITECTURE.md)

docs/security/deployment-model.md

@@ -0,0 +1,23 @@
+# Deployment Model — Single-Tenant by Design
+
+**The Solr MCP server is single-tenant. It does not support multi-tenancy.**
+
+The intended deployment is one instance per user, configured with that user's
+own Solr credentials. Every action the configured Solr identity is allowed to
+perform — including admin, schema, and collection operations — is by design
+reachable through the MCP tools. The server performs no per-user authorization
+or tenant isolation of its own; to limit what the tools can do, scope the Solr
+identity in Solr (Basic Auth, roles, mTLS, network policy).
+
+In HTTP mode, OAuth2 authenticates *that* a caller is allowed in, but every
+authenticated caller shares the same single Solr identity — it is an access
+gate, not a tenant boundary.
+
+Sharing one instance across multiple users, or otherwise treating it as
+multi-tenant, is unsupported: you are on your own for isolation and any
+resulting exposure. Multi-tenancy may be considered in a future release.
+
+## Related documents
+
+- [STDIO transport security model](./stdio.md)
+- [HTTP transport security model](./http.md)

docs/security/http.md

@@ -171,6 +171,7 @@ exists for browser-based tooling.
 
 ## Related documents
 
+- [Deployment model — single-tenant by design](./deployment-model.md)
 - [STDIO transport security model](./stdio.md)
 - OAuth2 provider setup: [Auth0](./auth0.md) · [Keycloak](./keycloak.md)
 - [GraalVM native image spec](../specs/graalvm-native-image.md)

docs/security/stdio.md

@@ -93,6 +93,7 @@ that launched the process. No code changes are required for STDIO security.
 
 ## Related documents
 
+- [Deployment model — single-tenant by design](./deployment-model.md)
 - [HTTP transport security model](./http.md)
 - OAuth2 provider setup (HTTP mode): [Auth0](./auth0.md) · [Keycloak](./keycloak.md)
 - [GraalVM native image spec](../specs/graalvm-native-image.md)