Add documentation for devices

Signed-off-by: Joas Schilling <coding@schilljs.com>

docs/push-v3.md

@@ -0,0 +1,186 @@
+# Push notifications as a Nextcloud client device
+
+
+
+## Checking the capabilities of the Nextcloud server
+
+In order to find out if notifications support push on the server you can run a request against the capabilities endpoint: `/ocs/v2.php/cloud/capabilities`
+
+```json
+{
+  "ocs": {
+    ...
+    "data": {
+      ...
+      "capabilities": {
+        ...
+        "notifications": {
+          "ocs-endpoints": [
+            ...
+            "push"
+          ]
+        }
+      }
+    }
+  }
+}
+```
+
+
+
+## Subscribing at the Nextcloud server
+
+1. **Only on first registration on the server** The device generates a `rsa2048` key pair (`devicePrivateKey` and `devicePublicKey`).
+
+2. The device generates the `PushToken` for *Apple Push Notification Service* (iOS) or *Firebase Cloud Messaging* (Android)
+
+3. The device generates a `sha512` hash of the `PushToken` (`PushTokenHash`)
+
+4. The device then sends the `devicePublicKey` and `PushTokenHash` to the Nextcloud server:
+
+   ```json
+   POST /ocs/v2.php/apps/notifications/api/v3/push
+
+   {
+     "pushTokenHash": "{{PushTokenHash}}",
+     "devicePublicKey": "{{devicePublicKey}}"
+   }
+   ```
+
+   ​
+
+### Response
+
+The server replies with the following status codes:
+
+| Status code | Meaning                                  |
+| ----------- | ---------------------------------------- |
+| 200         | No further action by the device required |
+| 201         | Push token was created/updated and **needs to be sent to the `Proxy`** |
+| 400         | Invalid public key, device does not use a token to authenticate or the push token hash is invalid formatted |
+| 401         | Device is not logged in                  |
+
+
+
+#### Body in case of success
+
+In case of `200` and `201` the reply has more information in the body:
+
+| Key              | Type         |                                          |
+| ---------------- | ------------ | ---------------------------------------- |
+| publicKey        | string (512) | rsa2048 public key of the user account on the instance |
+| deviceIdentifier | string (128) | unique identifier encrypted with the users private key |
+| signature        | string (512) | base64 encoded signature of the deviceIdentifier |
+
+
+
+#### Body in case of an error
+
+In case of `400` the following `message` can appear in the body:
+
+| Error                    | Description                              |
+| ------------------------ | ---------------------------------------- |
+| `INVALID_PUSHTOKEN_HASH` | The hash of the push token was not a valid `sha512` hash. |
+| `INVALID_SESSION_TOKEN`  | The authentication token of the request could not be identified. Check whether a password was used to login. |
+| `INVALID_DEVICE_KEY`     | The device key does not match the one registered to the provided session token. |
+
+
+
+## Unsubcribing at the Nextcloud server
+
+When an account is removed from a device, the device should unregister on the server. Otherwise the server sends unnecessary push notifications and might be blocked because of spam.
+
+
+
+The device should then send the `devicePublicKey` and `PushTokenHash` to the Nextcloud server: 
+
+```json
+DELETE /ocs/v2.php/apps/notifications/api/v3/push
+
+{
+  "devicePublicKey": "{{devicePublicKey}}"
+}
+```
+
+
+
+### Response
+
+The server replies with the following status codes:
+
+| Status code | Meaning                                  |
+| ----------- | ---------------------------------------- |
+| 202         | Push token was deleted and **needs to be deleted from the `Proxy`** |
+| 400         | Invalid public key or device does not use a token to authenticate |
+| 401         | Device is not logged in                  |
+
+
+
+#### Body in case of an error
+
+In case of `400` the following `message` can appear in the body:
+
+| Error                   | Description                              |
+| ----------------------- | ---------------------------------------- |
+| `INVALID_SESSION_TOKEN` | The authentication token of the request could not be identified. |
+| `INVALID_DEVICE_KEY`    | The device key does not match the one registered to the provided session token. |
+
+
+
+## Subscribing at the Push Proxy
+
+The device sends the`PushToken` as well as the `deviceIdentifier`, `signature` and the user´s `publicKey`  (from the server´s response) to the Push Proxy:
+
+```json
+POST /devices
+
+{
+  "pushToken": "{{PushToken}}",
+  "deviceIdentifier": "{{deviceIdentifier}}",
+  "deviceIdentifierSignature": "{{signature}}",
+  "userPublicKey": "{{userPublicKey}}"
+}
+```
+
+
+
+### Response
+
+The server replies with the following status codes:
+
+| Status code | Meaning                                  |
+| ----------- | ---------------------------------------- |
+| 200         | Push token was written to the databse    |
+| 400         | Push token, public key or device identifier is malformed, the signature does not match |
+| 403         | Device is not allowed to write the push token of the device identifier |
+| 409         | In case of a conflict the device can retry with the additional field `cloudId` with the value `{{userid}}@{{serverurl}}` which allows the proxy to verify the public key and device identifier belongs to the given user on the instance |
+
+
+
+## Unsubscribing at the Push Proxy
+
+The device sends the `deviceIdentifier` and the user´s `publicKey`  (from the server´s response) to the Push Proxy:
+
+```json
+DELETE /devices
+
+{
+  "deviceIdentifier": "{{deviceIdentifier}}",
+  "userPublicKey": "{{userPublicKey}}"
+}
+```
+
+
+
+### Response
+
+The server replies with the following status codes:
+
+| Status code | Meaning                                  |
+| ----------- | ---------------------------------------- |
+| 200         | Push token was deleted from the databse  |
+| 400         | Public key or device identifier is malformed |
+| 403         | Device identifier and device public key didn't match or could not be found |
+
+
+