update readme to reflect LKAPI interfaces (livekit#748)

Author: davidzhao

README.md

@@ -65,6 +65,21 @@ async def main():
 asyncio.run(main())
 ```
 
+### Authentication
+
+Authenticate with an API key and secret (recommended for backend use), or with a
+pre-signed token for client-side use, where the API secret must not be exposed.
+Any omitted value falls back to `LIVEKIT_URL`, `LIVEKIT_API_KEY`,
+`LIVEKIT_API_SECRET`, and `LIVEKIT_TOKEN`.
+
+```python
+# API key & secret (backend)
+lkapi = api.LiveKitAPI("https://my-project.livekit.cloud", api_key="...", api_secret="...")
+
+# pre-signed token (client-side); the token must already carry the grants for the calls
+lkapi = api.LiveKitAPI.with_token(my_token, "https://my-project.livekit.cloud")
+```
+
 ### Using other APIs
 
 Services can be accessed via the LiveKitAPI object.
@@ -91,6 +106,38 @@ dispatch_svc = lkapi.agent_dispatch
 connector_svc = lkapi.connector
 ```
 
+### Error handling
+
+A failed server API call raises `api.ServerError`, which exposes the error
+`code`, `message`, and any server-provided `metadata`.
+
+```python
+try:
+    await lkapi.room.create_room(api.CreateRoomRequest(name="my-room"))
+except api.ServerError as e:
+    print(e.code, e.message)
+```
+
+A failed SIP dial (e.g. the callee is busy or doesn't answer) raises
+`api.SipCallError`, a `ServerError` subclass that also exposes the SIP response
+status:
+
+```python
+try:
+    await lkapi.sip.create_sip_participant(api.CreateSIPParticipantRequest(
+        sip_trunk_id="ST_...",
+        sip_call_to="+15105550100",
+        room_name="my-room",
+        wait_until_answered=True,
+    ))
+except api.SipCallError as e:
+    print(e)                    # e.g. "SIP call failed: 486 Busy Here (resource_exhausted)"
+    if e.sip_status_code == 486:
+        ...                     # busy
+except api.ServerError as e:
+    print(e.code, e.message)    # any other API error
+```
+
 ## Using Real-time SDK
 
 ```shell

livekit-api/README.md

@@ -4,3 +4,26 @@ Access LiveKit server APIs and generate access tokens.
 
 See https://docs.livekit.io/reference/server/server-apis for more information.
 
+## Authentication
+
+Every request to the server APIs is authenticated. `LiveKitAPI` supports two modes:
+
+- **API key & secret** — recommended for backend use. The SDK signs a short-lived token per request from your key and secret. Keep your API secret on the server; never ship it to a client.
+- **Access token** — for client-side use where the API secret must not be exposed. Pass a pre-signed [access token](https://docs.livekit.io/home/get-started/authentication/) that already carries the grants for the operations you'll perform; the SDK sends it verbatim.
+
+```python
+from livekit import api
+
+# API key & secret: set LIVEKIT_URL, LIVEKIT_API_KEY, and LIVEKIT_API_SECRET,
+# then construct with no arguments...
+lkapi = api.LiveKitAPI()
+
+# ...or pass any of them explicitly to override the corresponding env var:
+lkapi = api.LiveKitAPI("https://my.livekit.host", api_key="api-key", api_secret="api-secret")
+
+# Pre-signed access token (client-side): with LIVEKIT_URL set, pass just the token:
+lkapi = api.LiveKitAPI.with_token("a-pre-signed-token")
+```
+
+The url and credentials fall back to the `LIVEKIT_URL`, `LIVEKIT_API_KEY`, `LIVEKIT_API_SECRET`, and `LIVEKIT_TOKEN` environment variables. Values you pass explicitly take precedence; the environment variables are used only as a fallback for arguments you omit — an ambient `LIVEKIT_TOKEN`, for example, won't override an explicitly-provided API key and secret.
+