diff --git a/docs/content/Deploying/Settings-Reference.mdx b/docs/content/Deploying/Settings-Reference.mdx
index 59b20430..88e4149d 100644
--- a/docs/content/Deploying/Settings-Reference.mdx
+++ b/docs/content/Deploying/Settings-Reference.mdx
@@ -1111,6 +1111,12 @@ Public callback URL for MCP OAuth; unset derives it from CONNECTOR_REDIRECT_BASE
 
 Serving the UI, public URLs, and process-level knobs of the API server.
 
+### `DEPLOYMENT_TYPE`
+
+Type `str`, default unset.
+
+Deployment class, e.g. cloud or production. A production class refuses to run without a configured JWT_SECRET_KEY instead of generating a local one on disk.
+
 ### `SERVE_UI`
 
 Type `bool`, default `true`.
diff --git a/docsgpt/app.py b/docsgpt/app.py
index 0913218f..4a11937e 100644
--- a/docsgpt/app.py
+++ b/docsgpt/app.py
@@ -1,5 +1,4 @@
 import logging
-import os
 import platform
 import uuid
 
@@ -170,16 +169,8 @@ def enforce_document_upload_request_size_limit():
 # only local development may use the atomic filesystem fallback.
 settings.JWT_SECRET_KEY = resolve_jwt_secret_key(
     settings.JWT_SECRET_KEY,
-    os.getenv("DEPLOYMENT_TYPE"),
+    settings.DEPLOYMENT_TYPE,
 )
-if settings.AUTH_TYPE == "oidc":
-    _missing_oidc = [
-        name
-        for name in ("OIDC_ISSUER", "OIDC_CLIENT_ID", "OIDC_FRONTEND_URL")
-        if not getattr(settings, name)
-    ]
-    if _missing_oidc:
-        raise RuntimeError(f"AUTH_TYPE=oidc requires settings: {', '.join(_missing_oidc)}")
 SIMPLE_JWT_TOKEN = None
 if settings.AUTH_TYPE == "simple_jwt":
     payload = {"sub": "local"}
diff --git a/docsgpt/core/settings/auth.py b/docsgpt/core/settings/auth.py
index 10e69801..04b039bc 100644
--- a/docsgpt/core/settings/auth.py
+++ b/docsgpt/core/settings/auth.py
@@ -4,11 +4,15 @@ from __future__ import annotations
 
 from typing import Literal, Optional
 
-from pydantic import Field, field_validator
+from pydantic import Field, field_validator, model_validator
 
 from docsgpt.core.settings._shared import SettingsGroup, normalize_choice, normalize_secret
 
 
+#: Settings an OIDC deployment cannot run without; checked when AUTH_TYPE=oidc.
+OIDC_REQUIRED = ("OIDC_ISSUER", "OIDC_CLIENT_ID", "OIDC_FRONTEND_URL")
+
+
 class AuthSettings(SettingsGroup):
     """How users authenticate: none, a shared token, per-session JWTs, or OIDC SSO."""
 
@@ -91,3 +95,11 @@ class AuthSettings(SettingsGroup):
     def _normalize_auth_type(cls, v):
         # ``AUTH_TYPE=None`` and ``AUTH_TYPE=`` in .env both mean "no authentication".
         return normalize_choice(normalize_secret(v))
+
+    @model_validator(mode="after")
+    def _require_oidc_settings(self):
+        if self.AUTH_TYPE == "oidc":
+            missing = [name for name in OIDC_REQUIRED if not getattr(self, name)]
+            if missing:
+                raise ValueError(f"AUTH_TYPE=oidc requires settings: {', '.join(missing)}")
+        return self
diff --git a/docsgpt/core/settings/server.py b/docsgpt/core/settings/server.py
index afb79121..407ef4aa 100644
--- a/docsgpt/core/settings/server.py
+++ b/docsgpt/core/settings/server.py
@@ -12,6 +12,13 @@ from docsgpt.core.settings._shared import SettingsGroup
 class ServerSettings(SettingsGroup):
     """Serving the UI, public URLs, and process-level knobs of the API server."""
 
+    DEPLOYMENT_TYPE: Optional[str] = Field(
+        default=None,
+        description=(
+            "Deployment class, e.g. cloud or production. A production class refuses to run without a "
+            "configured JWT_SECRET_KEY instead of generating a local one on disk."
+        ),
+    )
     SERVE_UI: bool = Field(
         default=True, description="Serve the web UI shipped in the package (docsgpt/static) from the API process."
     )
diff --git a/tests/core/test_settings.py b/tests/core/test_settings.py
index a4d64bf3..0757d8a4 100644
--- a/tests/core/test_settings.py
+++ b/tests/core/test_settings.py
@@ -110,6 +110,21 @@ class TestReference:
         )
 
 
+@pytest.mark.unit
+class TestCrossFieldRules:
+    OIDC = {"OIDC_ISSUER": "https://idp.example/", "OIDC_CLIENT_ID": "docsgpt", "OIDC_FRONTEND_URL": "http://app"}
+
+    def test_oidc_requires_issuer_client_and_frontend(self):
+        with pytest.raises(ValidationError, match="AUTH_TYPE=oidc requires settings: OIDC_CLIENT_ID, OIDC_FRONTEND_URL"):
+            Settings.model_validate({"AUTH_TYPE": "oidc", "OIDC_ISSUER": self.OIDC["OIDC_ISSUER"]})
+
+    def test_oidc_with_required_settings_loads(self):
+        assert Settings.model_validate({"AUTH_TYPE": "OIDC", **self.OIDC}).AUTH_TYPE == "oidc"
+
+    def test_oidc_settings_are_not_required_for_other_modes(self):
+        assert Settings.model_validate({"AUTH_TYPE": "session_jwt"}).OIDC_ISSUER is None
+
+
 @pytest.mark.unit
 class TestClosedChoices:
     """Enum-like settings are Literal types: a typo fails at startup instead of falling through."""
@@ -121,7 +136,7 @@ class TestClosedChoices:
     @pytest.mark.parametrize(
         ("name", "raw", "expected"),
         [
-            ("AUTH_TYPE", " OIDC ", "oidc"),
+            ("AUTH_TYPE", " Session_JWT ", "session_jwt"),
             ("VECTOR_STORE", "PGVector", "pgvector"),
             ("STORAGE_TYPE", "S3", "s3"),
             ("URL_STRATEGY", "Backend", "backend"),