How use a captive portal when in text mode?

Question

I've seen a few other questions where they show you how to connect to a network using bash, but I haven't seen anything where you connect to a captive portal network from the command line using Linux.

Is there a way to do login in a captive portal without being in graphics mode/having a Window manager?

Bash is a (common) Linux shell; can you clarify the distinction you’re after? — Jeff Schaller, Aug 25 '18 at 21:30
@JeffSchaller There are bash script floating around for automatic login in FON in Portugal (Nós operator), UK (BT) and Belgium. Some of them are obsolete. — Rui F Ribeiro, Aug 26 '18 at 12:26
Unfortunately there seems to be no standard implementation for captive portals: to implement a command-line-based connection method, you'd have to examine the source code of the portal page, and then design a solution for that specific portal, possibly using a tool like curl to submit the authentication information. — telcoM, Aug 26 '18 at 12:37
@telcoM For automating it using WISpr, you are right, but you can alway use lynx. Many captive portal implementations fall back to HTML only. Our FON network and the portal of our major ISP here does that, for instance. Interestingly enough, they have paid the guys that wrote the WISpr protocol big bucks. They are using their libraries behind their implementation. Which quite does not surprise me about our main operator, they have got plenty of money. — Rui F Ribeiro, Aug 26 '18 at 12:41
@JeffSchaller Sure, I was at the library running awesome wm and I was unable to connect to the internet because I couldn't open a captive portal browser window to agree to the library internet connection terms. I could get an ip address and everything using dhclient and theiwtools, but I couldn't get past those terms (also I don't know what the URL for them is), but I know it's possible because my Tablet had no trouble connecting. — leeand00, Aug 26 '18 at 15:36
I guess what I don't understand is, how does your machine know what the URL for the captive portal is? Is it a transparent proxy? Is it a firewall rule that changes after you click I agree? Can it be a number of things? — leeand00, Aug 26 '18 at 15:38
It always happens automatically on Windows, Android, and iOS, but with Linux it's always a gamble; so how does it work? Does DHCP send the URL as one of those special codes? — leeand00, Aug 26 '18 at 15:40
Really I just want to use my computer at the library without a memory hungry Window Manager. — leeand00, Aug 26 '18 at 15:41
Have you seen my answer? You do not need graphics to use lynx — Rui F Ribeiro, Aug 26 '18 at 16:05
@RuiFRibeiro Yeah I did sorry about that, just needed to refresh the browser that's all — leeand00, Aug 26 '18 at 16:29
Interestingly enough, questions about captive portals got a LOT of visits, both here in U&L and in StackOverlflow, as it is not a well understood functionality, especially on the server side. Many (re)implementations also only implement the captive/redirection part and do not implement WISpr. Being WISpr-aware portals automagically dealt with by Apple, Windows, Android and iOS only adds to the confusion of many people not knowing how to deal with captive portals when in less complex systems. — Rui F Ribeiro, Aug 26 '18 at 16:57

Rui F Ribeiro · Accepted Answer · 2018-08-26T18:03:38.207

As the underlying layers /Os is not talking WISpr/not running a program to deal with captive portals, for connecting to a captive portal in the command line, you only need a browser or a script.

One of the possible solutions is using lynx, a text mode browser.

It will work in most captive portals, and will allow you to enter your login and password to authenticate in the captive portal. I am not sure it is WISpr aware (i.e. a few rare portals where WISpr is mandatory)

In the past there were also bash scripts floating around for FON, they are not working nowadays. as in https://gist.github.com/cusspvz/3ab1ea9110f4ef87f0d2e1cd134aca67 or this one https://gist.github.com/itay-grudev/d3d4eb0dc4e239d96c84

A good clue how to write such a script can be seen here in python. However, you will have to adapt it to your specific needs.

https://github.com/Palakis/fortilogin

However for the majority of portals out there, lynx is fine.

See the related question Captive portal using Apache

For having an idea what is the WISpr tags I am talking about, see Getting WISPr tags from a FON authentication portal

For others reading this question, to be able to test a browser like Chrome , Firefox or lynx in a Mac authenticating in a portal, you need to disable CNA. See related Disabling CNA in MacOS

P.S. With the notable exception of major telecoms, and some wireless vendors like Ruckus (and a couple of ready-made captive portals like PfSense and CoovaChili), many (re)implementations of captive portals only implement the captive/redirection part and do not implement WISpr.

Being captive portals automagically dealt with by Apple, Windows, Android and iOS only adds to the confusion of many people not knowing how to deal with captive portals when in less complex systems because they have that nice layer of abstraction in more complex systems.

To deal with captive portals in systems not detecting them, you need to open a browser and hit reload/try to open a web page, to get presented with a page for accepting the provider clauses/ToS, and/or to get authenticated.

How use a captive portal when in text mode?

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