Traefik Plugin for Modifying Query Parameters

This Traefik plugin allows you to modify the query parameters of an incoming request, by either adding new, deleting or modifying existing query parameters. E.g. you can transform ?a=b&c=d&e=f to ?a=g&h=i by using this plugin (multiple times).

Sample Complete Configuration

The following code snippet is a sample configuration for the dynamic file based provider (TOML), but as usual, this plugin should work with all other configuration providers as well.

[http]
  [http.routers]
    [http.routers.router0]
      entryPoints = ["http"]
      service = "service-foo"
      rule = "Path(`/foo`)"
      middlewares = ["my-plugin"]

  [http.middlewares]
    [http.middlewares.my-plugin.plugin.dev]
      Type = "modify"
      ParamName = "password"
      NewValue = "censored"

Configuration Overview

This plugin knows three different modifications:

Adding new parameters (type = "add")

Specify the type (add), the name / key of the new query parameter (paramName) and the value of the new parameter (newValue).

Example:

type = "add"
paramName = "authenticated"
newValue = "true"

Transforms this querystring: ?some=other&stuff=here into: ?some=other&stuff=here&authenticated=true

Note: Existing query params with the same name are not replaced, instead a new param with the same name is added. Using the previous example: ?authenticated=false becomes ?authenticatd=false&authenticated=true. The handling of such query strings depends on your upstream server. To replace existing values, use modify.

Modifying existing parameters (type = "modify")

This is the most complex mode, as it supports multiple configuration types. You always need to specify which parameters to modify and how the new value should be computed. Avoid configuration more of one way for each of these (e.g. paramName and paramNameRegex) as this might result in unexpected behavior.

Specifying parameter

You have three choices:

• paramName matches the plain name / key of the parameter (e.g. paramName="test" matches the test=1234 param in ?test=1234&othertest=5678)
• paramNameRegex matches the name / key of the parameter with a regex (e.g. paramNameRegex="^.*test$" matches test=1234 and othertest=5678 in ?test=1234&othertest=5678)
• paramValueRegex matches the value of the parameter with a regex (e.g. paramValueRegex="^1234$" matches test=1234 in ?test=1234&othertest=5678)

Note: While always all matched parameters are handled, you might want to consider just using this middleware plugin multiple times instead of trying to create complex regexes for your situation.

Specifying substitution

There are two nays:

• newValue replaces the old value with the specifying value. $1 is replaced by the old value (note: as of now, this is not escapable) (e.g. paramName="test",newValue="bar-$1" transforms test=foo into test=bar-foo)
• newValueRegex allows you to use the capture groups from paramValueRegex to create the replacement value (e.g. paramValueRegex="^(.*)oo$",newValueRegex="$1" transforms test=foo&test2=poo into test=f&test=p)

Deleting existing parameters (type = "delete")

This deletes an existing parameters including all of it's values. Specifying the affected parameters works the same as above. Example: type="delete",paramValueRegex="password" transforms ?secret=password&othersecret=other-password&tracker=1234 into tracker=1234