Add wiki page on the LIHKG API version 2

[hk-ng]

Here is a example on common HTTP header after authentication:

HTTP header

Header	login user	used in browser	used in android	value	sample
x-li-device	x	✓	✓	sha1(UUID)	bd62c29291cbe9fb9662ef70f8c5042d55680f0
x-li-device-type	x	✓	✓	browser or android	browser
x-li-digest	✓	✓	✓	sha1(jeams${{http method in lower case}}${{url}}$${{user token}}${{value from x-li-request-time}})	82f1f6d46e14f73b088fbac68984aae5f157c971
x-li-load-time	x	✓	x	?????	4.3450985
x-li-plus	✓	✓	✓	?????	473672897fbc4c2447aefa76e69f26191e6385c1
x-li-request-time	✓	✓	✓	unix time stamp in UTC	1525597958
x-li-user	✓	✓	✓	user id

Note about x-li-digest:

The digest example was generated as following

name	value
{{http method in lower case}}	get
{{url}}	https://lihkg.com/api_v2/thread/634747/page/1?order=reply_time
{{user token}}	fc108e0701575efb4a70b69db2779860d02b9d33
{{value from x-li-request-time}}	1525597958

sha1( jeams${{http method in lower case}}${{url}}$${{user token}}${{value from x-li-request-time}} )
---> sha1( jeams$get$https://lihkg.com/api_v2/thread/634747/page/1?order=reply_time$$fc108e0701575efb4a70b69db2779860d02b9d33$1525597958 )
---> 82f1f6d46e14f73b088fbac68984aae5f157c971

With common HTTP header above, we can access the API after user login

[anthonylee1994]

It seems that the "x-li-digest" calculation has been changed, do you know how to get the new digest?

[hk-ng]

"x-li-digest" calculation is working for HTTP get request method.

lihkg android app will replace special character in url as following:
[ => %5b
] => %5d
, => %2c

I will confirm the map above later.

post method is a different story. The digest is like following:
sha1( jeams${{http method in lower case}}${{url}}${{convert post form data to query string}}${{user token}}${{value from x-li-request-time}} )
I dont know the order of post form data for query string and it will affect that sha1 hash. I will confirm the format of post method later.

[anthonylee1994]

I think the lihkg api checks the "x-li-digest" to determine whether the request is valid or not.

So, in order to allow us to create post or reply to post, we need to generate a valid "x-li-digest".

[hk-ng]

There is a WIP version of lihkg api client.
https://github.com/hk-ng/hkug/tree/master/lihkg-api