docs: add allowed_idp_claims docs (#1665)

docs/reference/readme.md

@@ -975,6 +975,41 @@ Allowed domains is a collection of whitelisted domains to authorize for a given
 Allowed groups is a collection of whitelisted groups to authorize for a given route.
 
 
+### Allowed IdP Claims
+- `yaml`/`json` setting: `allowed_idp_claims`
+- Type: map of `strings` lists
+- Required
+
+Allowed IdP Claims is a collection of whitelisted claim key-value pairs to authorize for a given route.
+
+This is useful if your identity provider has extra information about a user that is not in the directory.  It can also be useful if you wish to use groups with the generic OIDC provider.
+
+Example:
+
+```yaml
+  - from: http://from.example.com
+    to: http://to.example.com
+    allowed_idp_claims:
+      family_name:
+        - Doe
+        - Smith
+```
+
+This policy would match users with the `family_name` claim containing `Smith` or `Doe`.
+
+Claims are represented as a map of strings to a list of values:
+
+```json
+{
+  "family_name": ["Doe"],
+  "given_name": ["John"]
+}
+```
+
+- Nested maps are flattened: `{ "a": { "b": ["c"] } }` becomes `{ "a.b": ["c"] }`
+- Values are always a list: `{ "a": "b" }` becomes `{ "a": ["b"] }`
+
+
 ### Allowed Users
 - `yaml`/`json` setting: `allowed_users`
 - Type: list of `string`

docs/reference/settings.yaml

@@ -1087,6 +1087,44 @@ settings:
           - Example: `admins` , `support@company.com`
         doc: |
           Allowed groups is a collection of whitelisted groups to authorize for a given route.
+      - name: "Allowed IdP Claims"
+        keys: ["allowed_idp_claims"]
+        attributes: |
+          - `yaml`/`json` setting: `allowed_idp_claims`
+          - Type: map of `strings` lists
+          - Required
+        shortdoc: |
+          Authorize users by matching claims attached to a user's identity token by their identity provider
+        doc: |
+          Allowed IdP Claims is a collection of whitelisted claim key-value pairs to authorize for a given route.
+
+          This is useful if your identity provider has extra information about a user that is not in the directory.  It can also be useful if you wish to use groups with the generic OIDC provider.
+
+          Example:
+
+          ```yaml
+            - from: http://from.example.com
+              to: http://to.example.com
+              allowed_idp_claims:
+                family_name:
+                  - Doe
+                  - Smith
+          ```
+
+          This policy would match users with the `family_name` claim containing `Smith` or `Doe`.
+
+          Claims are represented as a map of strings to a list of values:
+
+          ```json
+          {
+            "family_name": ["Doe"],
+            "given_name": ["John"]
+          }
+          ```
+
+          - Nested maps are flattened: `{ "a": { "b": ["c"] } }` becomes `{ "a.b": ["c"] }`
+          - Values are always a list: `{ "a": "b" }` becomes `{ "a": ["b"] }`
+
       - name: "Allowed Users"
         keys: ["allowed_users"]
         attributes: |