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The following guide shows you how set the plugin up in the access phase.
In this example, the plugin will look for a request matching x-custom-auth
.
If the header exists in the request, it lets the request through.
If the header doesn’t exist, it terminates the request early.
Let’s test out the Pre-function plugin by filtering requests based on header names.
Set up the plugin
With a database
Without a database
-
Create a Kong Gateway service:
curl -i -X POST http://localhost:8001/services/ \
--data "name=example-service" \
--data "url=https://httpbin.konghq.com/headers"
-
Add a route to the service:
curl -i -X POST http://localhost:8001/services/example-service/routes \
--data "name=test" \
--data "paths[]=/test"
-
Create a file named custom-auth.lua
with the following content:
-- Get list of request headers
local custom_auth = kong.request.get_header("x-custom-auth")
-- Terminate request early if our custom authentication header
-- does not exist
if not custom_auth then
return kong.response.exit(401, "Invalid Credentials")
end
-- Remove custom authentication header from request
kong.service.request.clear_header('x-custom-auth')
-
Apply the Lua code using the pre-function
plugin endpoint:
curl -i -X POST http://localhost:8001/services/example-service/plugins \
--form "name=pre-function" \
--form "config.access[1]=@custom-auth.lua" \
--form "config.access[2]=kong.log.err('Test Access')" \
--form "config.header_filter[1]=kong.log.err('Test Header_Filter!')" \
--form "config.body_filter[1]=kong.log.err('Test Body_Filter!')" \
--form "config.log[1]=kong.log.err('Test Log!')"
If successful, the API returns a 201
response code.
-
Create the service, route, and associated plugin in the declarative config file:
services:
- name: example-service
url: https://httpbin.konghq.com/headers
routes:
- service: example-service
paths: [ "/test" ]
plugins:
- name: pre-function
config:
access:
- |2
-- Get list of request headers
local custom_auth = kong.request.get_header("x-custom-auth")
-- Terminate request early if the custom authentication header
-- does not exist
if not custom_auth then
return kong.response.exit(401, "Invalid Credentials")
end
-- Remove custom authentication header from request
kong.service.request.clear_header('x-custom-auth')
- kong.log.err('Test Access!')
header_filter:
- kong.log.err('Test Header_Filter!')
body_filter:
- kong.log.err('Test Body_Filter!')
log:
- kong.log.err('Test Log!')
-
Sync the file to your Kong Gateway instance:
deck gateway sync kong.yaml
Validate the code
-
Test that the code will terminate the request when no header is passed:
curl -i -X GET http://localhost:8000/test
You should get a 401
response:
HTTP/1.1 401 Unauthorized
...
"Invalid Credentials"
The logs will show the following messages:
[pre-function] Test Header_Filter!
[pre-function] Test Body_Filter!
[pre-function] Test Body_Filter!
[pre-function] Test Log!
The “Access” message is missing because the first function in that phase does
an early exit, throwing the 401. Hence the subsequent functions are not executed.
-
This time, test the code by making a valid request:
curl -i -X GET http://localhost:8000/test \
--header "x-custom-auth: demo"
You should get a 200
response:
Now the logs will also have the “Access” message.
This is just a small demonstration of the power this plugin grants. You were
able to dynamically inject Lua code into the plugin phases to dynamically
terminate, or transform the request without creating a custom plugin or
reloading and redeploying Kong Gateway.
In summary, serverless functions give you the full capabilities of a custom plugin
without requiring redeploying or restarting Kong.