When creating an endpoint using a malformed URL (in my case a URL with a missing type identifier of a used variable) the whole API is broken afterwards. The only way to fix the issue is to use SERVICE_ENDPOINT and SERVICE_TOKEN to remove the affected endpoint. After removing the affected endpoint everything is working like before.
I think it should be tested if a used URL is malformed or not before creating an endpoint.
stack@devstack002:~/devstack$ keystone endpoint-list
[...] (Everything is working fine in this case.)
stack@devstack002:~/devstack$ keystone endpoint-create --region RegionTesting --service 5c026f3ea65b42c28f19cc012616cdb6 --publicurl 'http://localhost:1234/$(tenant_id)s' --adminurl 'http://localhost:1234/$(tenant_id)s' --internalurl 'http://localhost:1234/$(tenant_id)'
+-------------+-------------------------------------+
| Property | Value |
+-------------+-------------------------------------+
| adminurl | http://localhost:1234/$(tenant_id)s |
| id | 1e4df8989cd648b9b25be71fa3ba612c |
| internalurl | http://localhost:1234/$(tenant_id) |
| publicurl | http://localhost:1234/$(tenant_id)s |
| region | RegionTesting |
| service_id | 5c026f3ea65b42c28f19cc012616cdb6 |
+-------------+-------------------------------------+
stack@devstack002:~/devstack$ keystone endpoint-list
Authorization Failed: Malformed endpoint URL (http://localhost:1234/$(tenant_id)), see ERROR log for details. (HTTP 500)
stack@devstack002:~/devstack$ keystone user-list
Authorization Failed: Malformed endpoint URL (http://localhost:1234/$(tenant_id)), see ERROR log for details. (HTTP 500)
stack@devstack002:~/devstack$ nova list
ERROR: Malformed endpoint URL (http://localhost:1234/$(tenant_id)), see ERROR log for details. (HTTP 500)
stack@devstack002:~/devstack$ glance image-list
Authorization Failed: Malformed endpoint URL (http://localhost:1234/$(tenant_id)), see ERROR log for details. (HTTP 500)
The internal URL is malformed in this case. The 's' is missing. It should be $(tenant_id)s instead of $(tenant_id).