server: templates: use relative URLs to refer to assets

[yanniszark]

Fixes #1553

This PR makes sure every template refers to its local assets using a URL relative to the request's URL.

For example:
server listens at localhost/dex so serverPath is dex
reqPath is /dex/auth
assetPath is static/main.css
relativeURL("/dex", "/dex/auth", "static/main.css") = "../static/main.css"

I had to propagate the request's path from each handler down to the templates' data.
I chose to pass the whole http request as a parameter to the template render functions, as it may contain other useful information in the future (eg values from context).
I can change it to only pass down the request's path if it's preferable.

Signed-off-by: Yannis Zarkadas yanniszark@arrikto.com

[yanniszark]

Hi @srenatus!
This PR is ready for a review whenever you have the time.
I wrote some unit tests for the new function that calculates the relative URL and I have also tested it in a Kubernetes cluster.

[yanniszark]

I just noticed that @srenatus is on parental leave. Sorry for the disturbance.

/cc @JoelSpeed @bonifaido @rithujohn191
Could you please take a look if possible?
This is something that we need for our use-case in integrating Dex with the Kubeflow project.

[JoelSpeed]

Seems sensible to me, one quick question, I don't mind this style just curious as to why you went for it 🙂

[JoelSpeed]

Any reason to define this and stripCommonParts as a local variable rather than an unexported method in the package?

[yanniszark]

Thanks a lot for the review @JoelSpeed 😄
I defined them as closures inside the relativeURL function because their scope was that specific function.
That is, they are not used elsewhere.

[JoelSpeed]

Fair enough 👍