README.md in fluent-plugin-bigquery-0.0.2 vs README.md in fluent-plugin-bigquery-0.0.3

@@ -7,26 +7,26 @@
   * https://developers.google.com/bigquery/streaming-data-into-bigquery#usecases
 * (NOT IMPLEMENTED) load data
   * for data loading as batch jobs, for big amount of data
   * https://developers.google.com/bigquery/loading-data-into-bigquery
   
-Current version of this plugin supports Google API with Service Account Authentication, and does not support OAuth.
+Current version of this plugin supports Google API with Service Account Authentication, but does not support
+OAuth flow for installed applications.
 
 ## Configuration
 
 ### Streming inserts
 
-For service account authentication, generate service account private key file and email key, then upload private key file onto your server.
-
 Configure insert specifications with target table schema, with your credentials. This is minimum configurations:
 
 ```apache
 <match dummy>
   type bigquery
   
   method insert    # default
   
+  auth_method private_key   # default
   email [e-mail]
   private_key_path /home/username/.keys/00000000000000000000000000000000-privatekey.p12
   # private_key_passphrase notasecret # default
   
   project yourproject_id
@@ -56,10 +56,11 @@
   buffer_chunk_records_limit 300  # default rate limit for users is 100
   buffer_queue_limit 10240        # 1MB * 10240 -> 10GB!
   
   num_threads 16
   
+  auth_method private_key   # default
   email [e-mail]
   private_key_path /home/username/.keys/00000000000000000000000000000000-privatekey.p12
   # private_key_passphrase notasecret # default
   
   project yourproject_id
@@ -97,9 +98,44 @@
     * 10 or more threads seems good for inserts over internet
     * less threads may be good for Google Compute Engine instances (with low latency for BigQuery)
   * `flush_interval`
     * `1` is lowest value, without patches on Fluentd v0.10.41 or earlier
     * see `patches` below
+
+### Authentication
+
+There are two methods supported to fetch access token for the service account.
+1. Public-Private key pair
+2. Predefined access token (Compute Engine only)
+
+The examples above use the first one.  You first need to create a service account (client ID),
+download its private key and deploy the key with fluentd.
+
+On the other hand, you don't need to explicitly create a service account for fluentd when you
+run fluentd in Google Compute Engine.  In this second authentication method, you need to
+add the API scope "https://www.googleapis.com/auth/bigquery" to the scope list of your
+Compute Engine instance, then you can configure fluentd like this.
+
+```apache
+<match dummy>
+  type bigquery
+  
+  auth_method compute_engine
+  
+  project yourproject_id
+  dataset yourdataset_id
+  table   tablename
+  
+  time_format %s
+  time_field  time
+  
+  field_integer time,status,bytes
+  field_string  rhost,vhost,path,method,protocol,agent,referer
+  field_float   requestime
+  field_boolean bot_access,loginsession
+</match>
+```
+
 
 ### patches
 
 This plugin depends on `fluent-plugin-buffer-lightening`, and it includes monkey patch module for BufferedOutput plugin, to realize high rate and low latency flushing. With this patch, sub 1 second flushing available.