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Block Unknown Email

Another important security note, is that BROWSER-ID will set authid and authidz to a valid email address. It does not (and cannot) confirm that this email address is meaningful in your system!

Any clients and servers that you BROWSER-ID enable MUST do this validation. Below are some common cases...

Worst Case

Let's say you have a resource 'keys-to-the-kingdom'. Before you depended on username and password. Calling 'get-keys-to-the-kingdom' would fail if a valid username/password combo were entered.

You add SASL BROWSER-ID. Calling 'get-keys-to-the-kingdom' always succeeds as long as the user submitted a valid verify email assertion and audience. Even if '' should not have been allowed access to 'keys-to-the-kingdom'.

How do we fix this?

Basically, we need to make sure that we've been authenticated as a valid user. How this is done will vary system by system.


  • Enforce ACL in your configuration
  • Enforce strict mapping of email address into valid accounts
  • Discover email address and make sure it's known
  • Have a 'new user' registration path for unknown users

So with our get-keys-to-the-kingdom function, we could query a database to make sure the email address exists in our user table.

The following tips are specific SASL enabled services:


Make sure your slapd.conf has ACL that restrict access to known users. Have a strict mapping for authentication identities.

Server Side

Example slapd.conf snippets:



Client Side

In code, use ldap's whoami function and ensure that the DN does not contain cn=browser-id.

If whoami is unavailable in your programming language, good ACL and a ACL test suite are critical.

Testing Notes

Make sure unknown email addresses fail when trying to search/add/modify/delete.

Make a test case where multiple records with the verified email address cause an auth failure. Search based mapping should have one and only one match for a known email address.

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