Support providing credentials via env var. (#27)

README.md

@@ -45,7 +45,7 @@ For other authentication method, please see Authentication section.
 
 ### Step 2: Install
 
-First, make sure Python 3 is installed on your system or follow these 
+First, make sure Python 3 is installed on your system or follow these
 installation instructions for Mac or Ubuntu.
 
 ```
@@ -62,7 +62,7 @@ pip install --no-cache-dir https://github.com/anelendata/tap-bigquery/archive/ma
 
 ### Step 1: Configure
 
-Create a file called tap_config.json in your working directory, following 
+Create a file called tap_config.json in your working directory, following
 config.sample.json:
 
 ```
@@ -150,6 +150,13 @@ It is recommended to use `tap-bigquery` with a service account.
 - Set a `GOOGLE_APPLICATION_CREDENTIALS` environment variable on the machine,
   where the value is the fully qualified path to client_secrets.json
 
+In environments where it is preferable to supply secrets or other configuration via
+environment variables or where it is not feasible to make a `client_secrets.json`
+file available, you may instead provide credential as a JSON string in the
+`GOOGLE_APPLICATION_CREDENTIALS_STRING` environment variable. This JSON string
+should contain the same contents and be formatted the same way as the contents
+of a `client_secrets.json` file.
+
 In the testing environment, you can also manually authenticate before runnig
 the tap. In this case you do not need `GOOGLE_APPLICATION_CREDENTIALS` defined:
 

tap_bigquery/sync_bigquery.py

@@ -2,6 +2,7 @@
 import dateutil.parser
 from decimal import Decimal
 
+from os import environ
 import singer
 import singer.metrics as metrics
 
@@ -11,6 +12,7 @@
 import getschema
 
 
+
 LOGGER = utils.get_logger(__name__)
 
 # StitchData compatible timestamp meta data
@@ -25,6 +27,19 @@
 
 BOOKMARK_KEY_NAME = "last_update"
 
+SERVICE_ACCOUNT_INFO_ENV_VAR = "GOOGLE_APPLICATION_CREDENTIALS_STRING"
+
+def get_bigquery_client():
+    """Initialize a bigquery client from credentials file JSON,
+    if in environment, else credentials file.
+
+    Returns:
+        Initialized BigQuery client.
+    """
+    credentials_json = environ.get(SERVICE_ACCOUNT_INFO_ENV_VAR)
+    if credentials_json:
+        return bigquery.Client.from_service_account_info(json.loads(credentials_json))
+    return bigquery.Client()
 
 def _build_query(keys, filters=[], inclusive_start=True, limit=None):
     columns = ",".join(keys["columns"])
@@ -63,7 +78,7 @@ def _build_query(keys, filters=[], inclusive_start=True, limit=None):
 
 def do_discover(config, stream, output_schema_file=None,
                 add_timestamp=True):
-    client = bigquery.Client()
+    client = get_bigquery_client()
 
     start_datetime = dateutil.parser.parse(
         config.get("start_datetime")).strftime("%Y-%m-%d %H:%M:%S.%f")
@@ -144,7 +159,7 @@ def do_sync(config, state, stream):
     singer.set_currently_syncing(state, stream.tap_stream_id)
     singer.write_state(state)
 
-    client = bigquery.Client()
+    client = get_bigquery_client()
     metadata = stream.metadata[0]["metadata"]
     tap_stream_id = stream.tap_stream_id