Tutorial

This tutorial aims to teach you how to make your own plugins.
If you just started dealing with Gateway and want to add a plugin to fulfill your deployment needs, then congradulations, you have come to the right place!
I have gone through a lot of pain trying to figure out how to write my JWT plugin. And thanks to the in-time replies of the maintainer and other members of the community, I finally made it. I wrapped up my weary and yet fruitful journey and published this tutorial in the hope that future newcomers have a detailed reference to look up.
If you encounter any problem going through the tutorial, feel free to create an issue or send me an email to this address brucewangno1@qq.com with the subject "Issues with Gateway Tutorial."

JWT Plugin Example

Before we dive into anything, I should tell you that pkg/proxy/filter_jwt.go is a properly working one with methods Pre() and Post(). You may modify it to suit your needs.
examples/jwt_a_simple_working_one.json, as its name suggests, is a simple working configuration which has one functionality - to check if the JWT is in the Redis server.
Add an JWT entry to your Redis server by redis-cli:

SET prefix_eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.G9-vbFqv8vkn91T028YcVOVId-wUF9kG5wIc2UgXxe4 true

prefix_ is in consistency with that in the JSON configuration file.

Start your proxy server with a command like the following:

./proxy --addr=127.0.0.1:80 --addr-rpc=127.0.0.1:9091 --addr-store=etcd://127.0.0.1:2379 --namespace=test --filter JWT --jwt "/some/path/leading/to/jwt_a_simple_working_one.json"

"this_is_jwt_secret" which appears in the JSON file is in the signature field in this JWT example.
Before we mock an API request from the client side, we have to go to the UI page and add this entry to take this all into effect. FYI, this makes c.API().AuthFilter in the Pre() method in pkg/proxy/filter_jwt.go JWT which matches f.Name().

Alright, alright, alright. This picture is self-explanatory.

Customize JWT Plugin

Since we are developing a JWT plugin to authenticate external requests, most of us have already had some working knowledge of JWT. If not, this official introduction is pretty informative. For Chinese developers, this link from Ruan Yifeng's blog is an excellent concise alternative.

Source Code Walk-through

pkg/filter/filter.go is pretty much an empty abstract from which *Filters structs in pkg/proxy/filter_*.go inherit the BaseFilter struct. For example, struct ValidationFilter only implementes methods Init(), Name(), and Pre(). These methods in BaseFilter are overridden and others remain available.
For JWT plugins, you should name your file like filter_my_plugin.go under pkg/proxy/ and refer to filter_plugin.go to write your own.
*.so plugin as mentioned in the docs/plugin.md, which involves cgo is really troublesome and thus highly discouraged.
After you have finished your plugin file, a plugin JSON configuration file is needed. For more information, please reference to this JSON configuration file example.
For your JWT plugin to take effect, you need to pass options --filter JWT and --jwt yourJSONConfigurationFilePath. This is because neither filter_jwt.go nor your plugin is in defaultFilters in pkg/proxy/proxy.go.
An example JWT JSON configuration file can be found in examples/jwt.json.
If one of the defaultFilters is expected to be used, please specify it by --filter like --filter WHITELIST when launching proxy because if there is --filter, defaultFilters gets discarded.