Implement application default credentials (#32)

diff --git a/tests/data/cloud_sdk.cfg b/tests/data/cloud_sdk.cfg
new file mode 100644
index 0000000..089aac5
--- /dev/null
+++ b/tests/data/cloud_sdk.cfg
@@ -0,0 +1,2 @@
+[core]
+project = example-project