diff --git a/docs/docs/configuration/authentication.md b/docs/docs/configuration/authentication.md
index 13638c511b..a27d86a80d 100644
--- a/docs/docs/configuration/authentication.md
+++ b/docs/docs/configuration/authentication.md
@@ -216,9 +216,9 @@ A default role can be provided. Any value in the mapped `role` header will overr
 
 Navigate to <NavPath path="Settings > System > Proxy" /> and set the default role.
 
-| Field            | Description                                                   |
-| ---------------- | ------------------------------------------------------------- |
-| **Default role** | Fallback role when no role header is present (e.g., `viewer`) |
+| Field            | Description                                                                                          |
+| ---------------- | ---------------------------------------------------------------------------------------------------- |
+| **Default role** | Fallback role when no role header is present (e.g., `viewer`), or `None (deny access)` to reject unmapped users |
 
 </TabItem>
 <TabItem value="yaml">
@@ -232,6 +232,14 @@ proxy:
 </TabItem>
 </ConfigTabs>
 
+Setting `default_role` to `none` denies access instead of falling back to a role. Any proxy-authenticated user whose headers do not match an explicit `role_map` entry receives a 403 response. This is useful when the upstream proxy authenticates a broader set of users than should reach Frigate, so that only mapped groups are allowed in.
+
+```yaml
+proxy:
+  ...
+  default_role: none
+```
+
 ## Role mapping
 
 In some environments, upstream identity providers (OIDC, SAML, LDAP, etc.) do not pass a Frigate-compatible role directly, but instead pass one or more group claims. To handle this, Frigate supports a `role_map` that translates upstream group names into Frigate's internal roles (`admin`, `viewer`, or custom). This is configurable via YAML in the configuration file:
@@ -257,7 +265,7 @@ In this example:
 - If the proxy passes a role header containing `sysadmins` or `access-level-security`, the user is assigned the `admin` role.
 - If the proxy passes a role header containing `camera-viewer`, the user is assigned the `viewer` role.
 - If the proxy passes a role header containing `operators`, the user is assigned the `operator` custom role.
-- If no mapping matches, Frigate falls back to `default_role` if configured.
+- If no mapping matches, Frigate falls back to `default_role` if configured, or denies access if `default_role` is `none`.
 - If `role_map` is not defined, Frigate assumes the role header directly contains `admin`, `viewer`, or a custom role name.
 
 **Note on matching semantics:**
@@ -331,7 +339,7 @@ Frigate supports user roles to control access to certain features in the UI and
 
 - **admin**: Full access to all features, including user management and configuration.
 - **viewer**: Read-only access to the UI and API, including viewing cameras, review items, and historical footage. Configuration editor and settings in the UI are inaccessible.
-- **Custom Roles**: Arbitrary role names (alphanumeric, dots/underscores) with specific camera permissions. These extend the system for granular access (e.g., "operator" for select cameras).
+- **Custom Roles**: Arbitrary role names (alphanumeric, dots/underscores) with specific camera permissions. These extend the system for granular access (e.g., "operator" for select cameras). The names `admin`, `viewer`, and `none` are reserved and cannot be used.
 
 ### Custom Roles and Camera Access
 
diff --git a/docs/static/frigate-api.yaml b/docs/static/frigate-api.yaml
index 5d0e0adbe0..0bfadd8331 100644
--- a/docs/static/frigate-api.yaml
+++ b/docs/static/frigate-api.yaml
@@ -62,6 +62,9 @@ paths:
                 type: string
         '401':
           description: Authentication Failed
+        '403':
+          description: Access Denied (proxy user resolved to a default role of 
+            'none')
       security: []
       x-required-role: public
   /profile:
diff --git a/frigate/api/auth.py b/frigate/api/auth.py
index 6d6ff30d4e..81c88d80fa 100644
--- a/frigate/api/auth.py
+++ b/frigate/api/auth.py
@@ -497,6 +497,7 @@ def resolve_role(
                      Admin matches short-circuit to admin.
                  - If no role_map is configured, treat the header as role names directly.
       2. If no valid role is found, return proxy_config.default_role if it's valid in config_roles, else 'viewer'.
+         The literal value 'none' is a valid default and means access should be denied.
 
     Args:
         headers (dict): Incoming request headers (case-insensitive).
@@ -509,10 +510,17 @@ def resolve_role(
     default_role = proxy_config.default_role
     role_header = proxy_config.header_map.role
 
-    # Validate default_role against config; fallback to 'viewer' if invalid
-    validated_default = default_role if default_role in config_roles else "viewer"
+    # Validate default_role against config; fallback to 'viewer' if invalid.
+    # "none" is a sentinel meaning "deny access when no mapping matches"; it is
+    # reserved in AuthConfig.validate_roles so it is never a configured role.
+    validated_default = (
+        default_role
+        if default_role in config_roles or default_role == "none"
+        else "viewer"
+    )
     if not config_roles:
-        validated_default = "viewer"  # Edge case: no roles defined
+        # Edge case: no roles defined
+        validated_default = "none" if default_role == "none" else "viewer"
 
     if not role_header:
         logger.debug(
@@ -617,6 +625,9 @@ def resolve_role(
             },
         },
         401: {"description": "Authentication Failed"},
+        403: {
+            "description": "Access Denied (proxy user resolved to a default role of 'none')"
+        },
     },
 )
 def auth(request: Request):
@@ -666,6 +677,10 @@ def auth(request: Request):
         config_roles_set = set(auth_config.roles.keys())
         role = resolve_role(request.headers, proxy_config, config_roles_set)
 
+        if role == "none":
+            logger.debug("Resolved role is 'none', denying access")
+            return Response("", status_code=403)
+
         success_response.headers["remote-role"] = role
 
         deny_status = deny_response_for_media_uri(original_url, role, frigate_config)
diff --git a/frigate/config/auth.py b/frigate/config/auth.py
index 04beeb7757..845ec45707 100644
--- a/frigate/config/auth.py
+++ b/frigate/config/auth.py
@@ -78,11 +78,14 @@ class AuthConfig(FrigateBaseModel):
                     f"Invalid role name '{role}'. Must be alphanumeric with underscores."
                 )
 
-        # Ensure 'admin' and 'viewer' are not used as custom role names
-        reserved_roles = {"admin", "viewer"}
-        if v.keys() & reserved_roles:
+        # 'none' is the deny sentinel for proxy.default_role, where it is matched
+        # case-insensitively, so every casing of it has to be reserved here
+        used_reserved = sorted(
+            r for r in v if r in ("admin", "viewer") or r.lower() == "none"
+        )
+        if used_reserved:
             raise ValueError(
-                f"Reserved roles {reserved_roles} cannot be used as custom roles."
+                f"Reserved role name(s) {', '.join(used_reserved)} cannot be used as custom roles."
             )
 
         # Ensure no role has an empty camera list
diff --git a/frigate/config/proxy.py b/frigate/config/proxy.py
index 196110520b..939585f62c 100644
--- a/frigate/config/proxy.py
+++ b/frigate/config/proxy.py
@@ -43,7 +43,7 @@ class ProxyConfig(FrigateBaseModel):
     default_role: str | None = Field(
         default="viewer",
         title="Default role",
-        description="Default role assigned to proxy-authenticated users when no role mapping applies.",
+        description="Default role assigned to proxy-authenticated users when no role mapping applies. Set to 'none' to deny access to unmapped users.",
     )
     separator: str | None = Field(
         default=",",
@@ -51,6 +51,16 @@ class ProxyConfig(FrigateBaseModel):
         description="Character used to split multiple values provided in proxy headers.",
     )
 
+    @field_validator("default_role", mode="before")
+    @classmethod
+    def normalize_deny_sentinel(cls, v):
+        # Fail closed on capitalization: an unnormalized "None" would miss the
+        # sentinel and fall back to viewer, granting the access it was meant to
+        # deny. Other role names stay case-sensitive.
+        if isinstance(v, str) and v.strip().lower() == "none":
+            return "none"
+        return v
+
     @field_validator("separator", mode="before")
     @classmethod
     def validate_separator_length(cls, v):
diff --git a/frigate/test/test_proxy_auth.py b/frigate/test/test_proxy_auth.py
index e4d2c9ce96..1833fd26b7 100644
--- a/frigate/test/test_proxy_auth.py
+++ b/frigate/test/test_proxy_auth.py
@@ -1,7 +1,9 @@
 import unittest
 
+from pydantic import ValidationError
+
 from frigate.api.auth import resolve_role
-from frigate.config import HeaderMappingConfig, ProxyConfig
+from frigate.config import AuthConfig, HeaderMappingConfig, ProxyConfig
 from frigate.config.env import FRIGATE_ENV_VARS
 
 
@@ -94,6 +96,137 @@ class TestProxyRoleResolution(unittest.TestCase):
         self.assertEqual(role, self.proxy_config.default_role)
 
 
+class TestDefaultRoleNone(unittest.TestCase):
+    def setUp(self):
+        self.proxy_config = ProxyConfig(
+            auth_secret=None,
+            default_role="none",
+            separator="|",
+            header_map=HeaderMappingConfig(
+                user="x-remote-user",
+                role="x-remote-role",
+                role_map={
+                    "admin": ["group_admin"],
+                    "viewer": ["group_viewer"],
+                },
+            ),
+        )
+        self.config_roles = list(["admin", "viewer"])
+
+    def test_default_role_none_no_match(self):
+        """Unmatched groups resolve to 'none' when default_role is 'none'."""
+        headers = {"x-remote-role": "group_unknown"}
+        role = resolve_role(headers, self.proxy_config, self.config_roles)
+        self.assertEqual(role, "none")
+
+    def test_default_role_none_with_match(self):
+        """Matched groups still resolve normally when default_role is 'none'."""
+        headers = {"x-remote-role": "group_admin"}
+        role = resolve_role(headers, self.proxy_config, self.config_roles)
+        self.assertEqual(role, "admin")
+
+    def test_default_role_none_missing_header(self):
+        """A missing role header resolves to 'none'."""
+        headers = {}
+        role = resolve_role(headers, self.proxy_config, self.config_roles)
+        self.assertEqual(role, "none")
+
+    def test_default_role_none_empty_header(self):
+        """An empty role header resolves to 'none'."""
+        headers = {"x-remote-role": ""}
+        role = resolve_role(headers, self.proxy_config, self.config_roles)
+        self.assertEqual(role, "none")
+
+    def test_default_role_none_no_role_map(self):
+        """An invalid direct role name resolves to 'none' without a role_map."""
+        config = ProxyConfig(
+            auth_secret=None,
+            default_role="none",
+            separator="|",
+            header_map=HeaderMappingConfig(
+                user="x-remote-user",
+                role="x-remote-role",
+                role_map=None,
+            ),
+        )
+        headers = {"x-remote-role": "notarole"}
+        role = resolve_role(headers, config, self.config_roles)
+        self.assertEqual(role, "none")
+
+    def test_default_role_none_no_role_header_configured(self):
+        """Proxy configs without a role header resolve to 'none'."""
+        config = ProxyConfig(
+            auth_secret=None,
+            default_role="none",
+            separator="|",
+            header_map=HeaderMappingConfig(user="x-remote-user"),
+        )
+        role = resolve_role({}, config, self.config_roles)
+        self.assertEqual(role, "none")
+
+    def test_default_role_none_no_roles_configured(self):
+        """'none' survives the empty config_roles edge case."""
+        headers = {"x-remote-role": "group_admin"}
+        role = resolve_role(headers, self.proxy_config, set())
+        self.assertEqual(role, "none")
+
+    def test_default_role_none_is_case_insensitive(self):
+        """Capitalized spellings must deny, not fall back to viewer."""
+        for spelling in ("None", "NONE", "nOnE", " none "):
+            with self.subTest(default_role=spelling):
+                config = ProxyConfig(
+                    auth_secret=None,
+                    default_role=spelling,
+                    separator="|",
+                    header_map=HeaderMappingConfig(
+                        user="x-remote-user",
+                        role="x-remote-role",
+                        role_map={"admin": ["group_admin"]},
+                    ),
+                )
+                self.assertEqual(config.default_role, "none")
+                role = resolve_role(
+                    {"x-remote-role": "group_unknown"}, config, self.config_roles
+                )
+                self.assertEqual(role, "none")
+
+    def test_other_role_names_stay_case_sensitive(self):
+        """Only the deny sentinel is normalized; role names are untouched."""
+        config = ProxyConfig(default_role="Operator")
+        self.assertEqual(config.default_role, "Operator")
+
+
+class TestReservedRoleNames(unittest.TestCase):
+    def test_reserved_names_rejected(self):
+        """admin, viewer, and the 'none' deny sentinel cannot be custom roles."""
+        for name in ("admin", "viewer", "none"):
+            with self.subTest(role=name):
+                with self.assertRaises(ValidationError):
+                    AuthConfig(roles={name: ["front_door"]})
+
+    def test_custom_role_still_allowed(self):
+        config = AuthConfig(roles={"operator": ["front_door"]})
+        self.assertEqual(config.roles["operator"], ["front_door"])
+
+    def test_error_names_the_offending_role(self):
+        """The message must say which name to rename, in a stable order."""
+        with self.assertRaises(ValidationError) as ctx:
+            AuthConfig(roles={"none": ["front_door"], "admin": ["front_door"]})
+        self.assertIn("admin, none", str(ctx.exception))
+
+    def test_none_reserved_in_every_casing(self):
+        """proxy.default_role folds case, so a 'None' role would be unreachable."""
+        for name in ("None", "NONE", "nOnE"):
+            with self.subTest(role=name):
+                with self.assertRaises(ValidationError):
+                    AuthConfig(roles={name: ["front_door"]})
+
+    def test_case_variant_of_a_normal_role_still_allowed(self):
+        """Only 'none' folds case; other role names are untouched."""
+        config = AuthConfig(roles={"Operator": ["front_door"]})
+        self.assertEqual(config.roles["Operator"], ["front_door"])
+
+
 class TestProxyAuthSecretEnvString(unittest.TestCase):
     def setUp(self):
         self._original_env_vars = dict(FRIGATE_ENV_VARS)
diff --git a/web/public/locales/en/config/global.json b/web/public/locales/en/config/global.json
index af1ed4fcbe..b9149dd203 100644
--- a/web/public/locales/en/config/global.json
+++ b/web/public/locales/en/config/global.json
@@ -212,7 +212,7 @@
     },
     "default_role": {
       "label": "Default role",
-      "description": "Default role assigned to proxy-authenticated users when no role mapping applies."
+      "description": "Default role assigned to proxy-authenticated users when no role mapping applies. Set to 'none' to deny access to unmapped users."
     },
     "separator": {
       "label": "Separator character",
diff --git a/web/public/locales/en/views/settings.json b/web/public/locales/en/views/settings.json
index 32338a0e92..44d8bfb609 100644
--- a/web/public/locales/en/views/settings.json
+++ b/web/public/locales/en/views/settings.json
@@ -1738,7 +1738,8 @@
     },
     "defaultRole": {
       "admin": "Admin",
-      "viewer": "Viewer"
+      "viewer": "Viewer",
+      "none": "None (deny access)"
     }
   },
   "globalConfig": {
diff --git a/web/src/components/config-form/theme/widgets/DefaultRoleWidget.tsx b/web/src/components/config-form/theme/widgets/DefaultRoleWidget.tsx
index a8925784a7..d79cd7d4e8 100644
--- a/web/src/components/config-form/theme/widgets/DefaultRoleWidget.tsx
+++ b/web/src/components/config-form/theme/widgets/DefaultRoleWidget.tsx
@@ -12,6 +12,7 @@ import type { ConfigFormContext } from "@/types/configForm";
 import { getSizedFieldClassName } from "../utils";
 
 const BUILT_IN_ROLES = ["admin", "viewer"];
+const NONE_ROLE = "none";
 
 export function DefaultRoleWidget(props: WidgetProps) {
   const { id, value, disabled, readonly, onChange, schema, options, registry } =
@@ -25,13 +26,15 @@ export function DefaultRoleWidget(props: WidgetProps) {
     const configured = Object.keys(formContext?.fullConfig?.auth?.roles ?? {});
     // Keep admin/viewer first, then any custom roles in config order.
     const custom = configured.filter((r) => !BUILT_IN_ROLES.includes(r));
-    return [...BUILT_IN_ROLES, ...custom];
+    return [...BUILT_IN_ROLES, ...custom, NONE_ROLE];
   }, [formContext]);
 
   const selectedValue = typeof value === "string" && value ? value : "viewer";
 
   const getLabel = (role: string) =>
-    BUILT_IN_ROLES.includes(role) ? t(`configForm.defaultRole.${role}`) : role;
+    BUILT_IN_ROLES.includes(role) || role === NONE_ROLE
+      ? t(`configForm.defaultRole.${role}`)
+      : role;
 
   return (
     <Select