diff --git a/cloud/api/iam.proto b/cloud/api/iam.proto
new file mode 100644
index 0000000..2bfc4ed
--- /dev/null
+++ b/cloud/api/iam.proto
@@ -0,0 +1,18 @@
+syntax = "proto3";
+package cloud.api;
+option go_package = "source.monogon.dev/cloud/api";
+
+service IAM {
+  rpc WhoAmI(WhoAmIRequest) returns (WhoAmIResponse);
+}
+
+message WhoAmIRequest {
+}
+
+message WhoAmIResponse {
+  // Opaque identifier (eg. UUID) of the acting account. Immutable.
+  string account_id = 1;
+  // Primary email address of the acting account. Can change, must not be used
+  // as a foreign key in other systems.
+  string email = 2;
+}
\ No newline at end of file