gitlab: triggering workflow fails with KeyError: 'workflow'

[mdonadoni]

Reported to us on mattermost and reproduced on PROD.

When GitLab triggers a new workflow via webhooks, the workflow creation process sometimes fails. This is the response coming from REANA, as shown on GitLab webhook test page (400):

{
  "message": "'workflow'"
}

reana-server logs:

  File "/code/./reana_server/rest/workflows.py", line 531, in create_workflow
    workflow_engine = reana_spec_file["workflow"]["type"]
KeyError: 'workflow'

The issue is probably that we are not checking whether the request to fetch the workflow specification is successful:

reana-server/reana_server/utils.py

Lines 450 to 459 in fbf6ba1

	yaml_file = requests.get(
	gitlab_api.format(project_id, reana_yaml, branch, gitlab_token)
	)
	return (
	yaml.load(yaml_file.content, Loader=yaml.FullLoader),
	webhook_data["project"]["path_with_namespace"],
	webhook_data["project"]["name"],
	branch,
	commit_sha,
	)

This is the response of the request:

{"error":"invalid_token","error_description":"Token is expired. You can either do re-authorization or token refresh."}