I had to figure this out for one of my clients who needed a client portal login.
Here's what I did. The link that I provided for the login was one which simply added a record to a table.
https://mycompany.quickbase.com/db/xxxxxxxxx?a=nwr&ifv=1
The suffix of &ifv=1 hides all the Quickbase branding. Since it is just an Add record form, I was able to put my clients' logo on the Add Record Form.
Note that I'm really just adding a record to a dummy table in order to be able to get their credentials
So now the user sitting on the form and has filled out their user ID and password.
I have to get the cursor to jump out of the password field, so I made a check box field on the form with some dummy words like I'm not a robot or I accept the "MyClient" terms and conditions. The Checkbox doesn't do anything other than get the cursor out of the previous field.
Then, once that checkbox is checked, I expose a URL formula button to login with this code.
var text Authenticate = URLRoot() & "db/main?a=API_Authenticate"
& "&username=" & URLEncode([Userid])
& "&password=" & URLEncode([Password]);
var text Portal = "https://mycompany.quickbase.com/db/xxxxxxxx?a=q&qid=15&ifv=1";
var text URL =
$Authenticate
& "&rdr=" & URLEncode($Portal);
$URL
So what the URL does is to login and then redirect the user to whatever URL you want. In my case I wanted to land the user on a particular report.
I also wanted to hide the Quickbase branding all the way through so each URL that we provide the user to click on has that same suffix to suppress the Quickbase branding.