docs: Add Proxmox instructions

Add Proxmox instructions for both running tsidp and using tsidp.
 
Co-authored-by: Remy Guercio <[email protected]>

Author: dfcarney

README.md

@@ -172,7 +172,9 @@ tsidp can be used as IdP server for any application that supports custom OIDC pr
 > [!IMPORTANT]
 > Note: If you'd like to use tsidp to login to a SaaS application outside of your tailnet rather than a self-hosted app inside of your tailnet, you'll need to run tsidp with `--funnel` enabled.
 
-- (TODO) Proxmox
+- [Proxmox](docs/proxmox/README.md)
+
+### TODOs
 - (TODO) Grafana
 - (TODO) open-webui
 - (TODO) Jellyfin

docs/proxmox/README.md

@@ -0,0 +1,162 @@
+# Proxmox Setup with tsidp
+
+This section covers:
+- Deploying tsidp in a Docker container within a Linux Container (LXC)
+- Configuring Proxmox to use tsidp for authentication
+
+## Deploy tsidp in Docker within an LXC
+
+### Prerequisites
+
+Before starting, download an LXC template:
+- See the [Proxmox Linux Container documentation](https://pve.proxmox.com/wiki/Linux_Container) for details
+- For video guidance, see [this tutorial](https://www.youtube.com/watch?v=iIfRchzYSzM&t=300s) by [Christian Lempa](https://www.youtube.com/@christianlempa)
+- This guide uses `alpine-3.21-default_20241217_amd64.tar.xz`, though other templates should work
+
+### Create the LXC
+
+1. **Log in to Proxmox** and create a new LXC (we'll name it `tsidp-lxc`, but any name works)
+
+   ![Create LXC](create-lxc.png)
+
+2. **Configure the container** with these settings:
+   - **General**
+     - ✅ Enable "Unprivileged container"
+     - ✅ Enable "Nesting" (required for Docker)
+   - **Template**
+     - Select `alpine-3.21-default_20241217_amd64.tar.xz`
+   - **Disks**
+     - Disk size: 4 GiB
+   - **CPU**
+     - Cores: 1
+   - **Memory**
+     - Memory: 512 MiB
+     - Swap: 512 MiB
+   - **Network**
+     - Use default settings
+   - **DNS**
+     - Use default settings
+   - **Confirm**
+     - ✅ Enable "Start after created"
+     - Click "Finish"
+
+   > **Note**: We're not enabling `keyctl=1` as tsidp doesn't use Docker secrets.
+
+### Set Up Docker and tsidp
+
+1. **Access the container console** in Proxmox
+   - Log in as `root` with the password you specified
+
+2. **Update packages and install dependencies**
+   ```bash
+   apk update
+   apk add docker git
+   ```
+
+3. **Start and enable Docker**
+   ```bash
+   rc-service docker start
+   rc-update add docker boot
+   ```
+   > You may see warnings, but should see `* Starting Docker Daemon ... [ ok ]`
+
+4. **Verify Docker installation**
+   ```bash
+   docker --version
+   ```
+
+5. **Clone the tsidp repository**
+   ```bash
+   mkdir -p /usr/local/src && cd /usr/local/src
+   git clone https://github.com/tailscale/tsidp.git
+   ```
+
+6. **Build and run tsidp**
+   - Follow the [Building your own container](../../README.md) instructions to launch tsidp inside of a Docker container in the LXC
+
+### Configure Auto-start
+
+Once `https://idp...` is working:
+
+1. **Enable Docker container auto-restart**
+   ```bash
+   docker update --restart unless-stopped tsidp
+   ```
+
+2. **Enable LXC auto-start** in Proxmox UI:
+   - Select the container
+   - Go to Options → Set "Start at boot" to "Yes"
+
+3. **Test the configuration** by rebooting the LXC and/or Proxmox server
+
+## Configure Proxmox to Use tsidp
+
+This example assumes:
+- Proxmox server: `https://scruggs.yourtailnet.ts.net:8006`
+- tsidp instance: `https://idp.yourtailnet.ts.net`
+
+### Register Proxmox as a Client in tsidp
+
+1. **Visit** `https://idp.yourtailnet.ts.net` and click "Add New Client"
+
+   ![Add New Client](add-oidc-client.png)
+   
+2. **Configure the client**:
+   - Add redirect URIs for each way you access Proxmox
+   - Save the generated Client ID and Client Secret; you'll use these next
+
+   ![Configure the client](tsidp-multiple-uri-redirects.png)
+
+### Configure OpenID Connect in Proxmox
+
+1. **Navigate to** Datacenter → Permissions → Realms -> **Add an OpenID Connect Server**
+
+   ![Create Realm](create-realm.png)
+
+2. **Configure the OpenID Connect Server realm** with these settings:
+   - **Issuer URL**: `https://idp.yourtailnet.ts.net`
+   - **Realm**: `tailscale` (or your preferred name)
+   - **Client ID**: (from tsidp)
+   - **Client Secret**: (from tsidp)
+   - **Default**: Yes
+   - **Autocreate Users**: Yes
+   - **Username Claim**: `email`
+
+   ![OpenID Connect Server Configuration](configure-realm.png)
+
+### Test the Authentication
+
+1. **Open an incognito browser window** and navigate to `https://scruggs.yourtailnet.ts.net:8006`
+
+2. **Log in** using the `tailscale` realm
+   - Authentication should work immediately
+   - Proxmox will auto-create a user account (due to "Autocreate Users: yes")
+   - However, this user account will have no permissions.
+
+   ![Login with Tailscale Realm](login-using-tailscale-realm.png)
+
+3. **Close the incognito window**
+
+### Assign User Permissions
+
+1. **Create an admin group**:
+   - Go to Datacenter → Permissions → Groups
+   - Create a group called `tsadmins`
+
+2. **Grant administrator privileges**:
+   - Go to Datacenter → Permissions
+   - Add a Group Permission:
+     - **Path**: `/`
+     - **Group**: `tsadmins`
+     - **Role**: `Administrator`
+
+    ![Group Permission Configuration](add-group-permission.png)
+
+3. **Add users to the admin group**:
+   - Go to Datacenter → Permissions → Users
+   - Edit the auto-created user
+   - Add them to the `tsadmins` group
+
+## Final Verification
+
+Log out of Proxmox and log back in using the new Tailscale realm to verify everything is working correctly.