docs: add synology dsm docs (#4167)

docs/content/en/integration/openid-connect/synology-dsm/index.md

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+---
+title: "Synology DSM"
+description: "Integrating Synology DSM with the Authelia OpenID Connect Provider."
+lead: ""
+date: 2022-06-15T17:51:47+10:00
+draft: false
+images: []
+menu:
+integration:
+parent: "openid-connect"
+weight: 620
+toc: true
+community: true
+---
+
+## Tested Versions
+
+* [Authelia]
+  * [v4.35.6](https://github.com/authelia/authelia/releases/tag/v4.35.6)
+* [Synology DSM]
+  * v7.1
+
+## Before You Begin
+
+You are required to utilize a unique client id and a unique and random client secret for all [OpenID Connect] relying
+parties. You should not use the client secret in this example, you should randomly generate one yourself. You may also
+choose to utilize a different client id, it's completely up to you.
+
+*__Important Note:__ [Synology DSM] does not support automatically creating users via [OpenID Connect]. It is therefore
+recommended that you ensure Authelia and [Synology DSM] share a LDAP server.*
+
+This example makes the following assumptions:
+
+* __Application Root URL:__ `https://dsm.example.com/`
+* __Authelia Root URL:__ `https://auth.example.com`
+* __Client ID:__ `synology-dsm`
+* __Client Secret:__ `synology-dsm_client_secret`
+
+## Configuration
+
+### Application
+
+To configure [Synology DSM] to utilize Authelia as an [OpenID Connect] Provider:
+
+1. Go to DSM.
+2. Go to `Control Panel`.
+3. Go To `Domain/LDAP`.
+4. Go to `SSO Client`.
+5. Check the `Enable OpenID Connect SSO service` checkbox in the `OpenID Connect SSO Service` section.
+6. Configure the following values:
+    * Profile: `OIDC`
+    * Name: `Authelia`
+    * Well Known URL: `https://auth.example.com/.well-known/openid-configuration`
+    * Application ID: `synology-dsm`
+    * Application Key: `synology-dsm_client_secret`
+    * Redirect URL: `https://dsm.example.com`
+    * Authorisation Scope: `openid profile groups email`
+    * Username Claim: `preferred_username`
+7. Save the settings.
+
+{{< figure src="client.png" alt="Synology" width="736" >}}
+
+### Authelia
+
+The following YAML configuration is an example __Authelia__
+[client configuration](../../../configuration/identity-providers/open-id-connect.md#clients) for use with [Synology DSM]
+which will operate with the above example:
+
+```yaml
+- id: synology-dsm
+  description: Synology DSM
+  secret: synology-dsm_client_secret
+  public: false
+  authorization_policy: two_factor
+  redirect_uris:
+    - https://dsm.example.com
+  scopes:
+    - openid
+    - profile
+    - groups
+    - email
+  userinfo_signing_algorithm: none
+```
+
+## See Also
+
+* [Synology DSM SSO Client Documentation](https://kb.synology.com/en-af/DSM/help/DSM/AdminCenter/file_directory_service_sso?version=7)
+
+[Authelia]: https://www.authelia.com
+[Synology DSM]: https://www.synology.com/en-global/dsm
+[OpenID Connect]: ../../openid-connect/introduction.md