fix: s3 backend deprecated role_arn field (#151)

Author: basvandijk

templates/terraform.tf.tpl

@@ -2,14 +2,19 @@ terraform {
   required_version = ">= ${terraform_version}"
 
   backend "s3" {
-    region   = "${region}"
-    bucket   = "${bucket}"
-    key      = "${terraform_state_file}"
-    profile  = "${profile}"
-    role_arn = "${role_arn}"
-    encrypt  = "${encrypt}"
+    region  = "${region}"
+    bucket  = "${bucket}"
+    key     = "${terraform_state_file}"
+    profile = "${profile}"
+    encrypt = "${encrypt}"
+    %{~ if role_arn != "" ~}
 
+    assume_role {
+      role_arn = "${role_arn}"
+    }
+    %{~ endif ~}
     %{~ if dynamodb_table != "" ~}
+
     dynamodb_table = "${dynamodb_table}"
     %{~ endif ~}
   }