How to set up multi key-auth for different routes

[Lang Wang <to...@apache.org>]

I see the key-auth plugin doc from
https://github.com/apache/incubator-apisix/blob/master/doc/plugins/key-auth-cn.md
says that:

curl -i http://127.0.0.1:9180/apisix/admin/consumers -X PUT -d '
{
    "username": "jack",
    "plugins": {
        "key-auth": {
            "key": "auth-one"
        }
    }
}'

curl -i http://127.0.0.1:9180/apisix/admin/routes/115 -X PUT -d '
{
    "methods": ["GET","HEAD"],
    "uri": "/kat",
    "plugins": {
        "key-auth": {}
    },
    "upstream": {
        "type": "roundrobin",
        "nodes": {
            "127.0.0.1:8086": 10
        }
    }
}'

# curl -I http://127.0.0.1:9080/kat -H 'apikey: auth-one'
HTTP/1.1 404 Not Found

# curl -I http://127.0.0.1:9080/kat
HTTP/1.1 401 Unauthorized


curl -i http://127.0.0.1:9180/apisix/admin/consumers -X PUT -d '
{
    "username": "jack1",
    "plugins": {
        "key-auth": {
            "key": "auth-one1"
        }
    }
}'

curl -i http://127.0.0.1:9180/apisix/admin/routes/116 -X PUT -d '
{
    "methods": ["GET","HEAD"],
    "uri": "/kat1",
    "plugins": {
        "key-auth": {}
    },
    "upstream": {
        "type": "roundrobin",
        "nodes": {
            "127.0.0.1:8086": 10
        }
    }
}'


# curl -I http://127.0.0.1:9080/kat1
HTTP/1.1 401 Unauthorized

# curl -I http://127.0.0.1:9080/kat1 -H 'apikey: auth-one1'
HTTP/1.1 404 Not Found

# curl -I http://127.0.0.1:9080/kat1 -H 'apikey: auth-one'
HTTP/1.1 404 Not Found


----

Now using `apikey: auth-one` and 'apikey: auth-one1'  in header could
access url `http://127.0.0.1:9080/kat1` and `http://127.0.0.1:9080/kat`.
How to set up key-auth rules just like :

`apikey: auth-one` ----> `http://127.0.0.1:9080/kat` ----> http 200
                              ----> `http://127.0.0.1:9080/kat1` ----> http
401

`apikey: auth-one1` ----> `http://127.0.0.1:9080/kat1` ----> http 200
                              ----> `http://127.0.0.1:9080/kat` ----> http
401

What's more, why we should set a blank key-auth plugin for routes like:

    "plugins": {
        "key-auth": {}
    }

other than:

    "plugins": {
        "key-auth": "jack" # or "jack1" from `username` of consumers
    }