Cleanest way to hide password input fields? - asp.net

Question

We have some error reporting code that, when an unhandled exception occurs, we send everything over in an email to our groups. This is great except if an unhandled exception occurs on a page with a password field then it's sent over as plain text.
Is there a way to iterate through Request.Form and figure out which item(s) are passwords? This is done at a low level so we can't look for specific controls.
Naturally, we could check to see what type the input box is but I'm not sure if that's the cleanest way. Advice?

Answer 1

Use a whitelist of field names that you want to email.
There could be hundreds of field names that get POSTed to your server. And password isn't the only field that is sensitive. Depending on your application, there could be other things that should be treated with a little respect.
So, make a list of field names that will assist in you in debugging. These are typically unique identifiers / database keys and such. If you have any parameter names in this list, you can include it in the email.

Answer 2

I've suggested a different solution earlier, but I thought you were going to handle this on the client side. Following your comments I now understand that you need to take care of this on the server side. There may be a way for you to do it, which is not really elegant, but it should work:
Add to all pages a script that collects all password field names into a new client-generated field, like so:
function collectPasswordFields() {
var inputs = document.getElementsByTagName('input'), list = [];
for (var i = 0; i < inputs.length; ++i)
if (inputs[i].type == 'password') list.push(inputs[i].name);
var field = document.createElement('input');
field.name = '__password_fields';
field.value = list.join(',');
document.getElementsByTagName('form')[0].appendChild(field);
}
Then intercept the additional field in the server-side error handler, and remove the named fields from the email.
Can something like this work for you?

Answer 3

The cleanest way is to check the type attribute of the input element.
The HTML5 specification has this to say about input type=password:
The input element with a type attribute whose value is "password" represents a one-line plain-text edit control for entering a password.
Data type: Text with no line breaks (sensitive information)
Control type: Text field that obscures data entry
This is a mandatory requirement from all User Agent implmentations, and it has been so since HTML 2. So this is indeed the cleanest way to do what you want.
If you want to do it on the client side (you talked about sending the data to the server) then it is relatively easy:
function hidePasswords() {
var inputs = document.getElementsByTagName('input');
for (var i = 0; i < inputs.length; ++i)
if (inputs[i].type == 'password') input[i].value = '*****';
}

Answer 4

As Jerome already pointed out in the comments, just keep track of the names of your password input fields and filter them before sending the error/exception report. This is the best solution as the type of the input field is not submitted.

Answer 5

A few solutions, though I'm not sure how bright any of them is:
1) Maintain in the page a List of input control IDs that are passwords, pass this list to the exception handler with the expectation to ignore these fields.
2) Keep a resource file in the website that lists a page name, a field id and have the exception handler check against this resource file (may not work if the exception is related to the ResourceManager)
3) Keep a database table as with idea 2. Same problems exist.