Document OpenID (#80)

README.md

@@ -19,6 +19,7 @@ In order to use Browserpass you must also install a [companion native messaging
     -   [First steps in browser extension](#first-steps-in-browser-extension)
     -   [Available keyboard shortcuts](#available-keyboard-shortcuts)
     -   [Password matching and sorting](#password-matching-and-sorting)
+    -   [OpenID authentication](#openid-authentication)
     -   [Modal HTTP authentication](#modal-http-authentication)
     -   [Password store locations](password-store-locations)
 -   [Options](#options)
@@ -99,6 +100,8 @@ Browserpass was designed with an assumption that certain conventions are being f
 
 1. Username must be defined on a line starting with `login:`, `username:`, `user:` or `email:` (case-insensitive), and if all of these are absent, default username as configured in browser extension or in `.browserpass.json` of specific password store, and finally if everything is absent the file name is considered to be a username.
 
+1. OpenID URL must be defined on a line starting with `openid:` (case-insensitive).
+
 1. URL ([only](#password-matching-and-sorting) used for [modal HTTP authentication](#modal-http-authentication)!) must be defined on a line starting with `url:`, `uri:`, `website:`, `site:`, `link:` or `launch:` (case-insensitive).
 
 ### First steps in browser extension
@@ -152,6 +155,10 @@ The sorting algorithm implemented in Browserpass will use several intuitions to
 1. Password entries with the identical usage counts are sorted by number of domain levels (specificity), i.e. `wiki.example.com` will be above `example.com`.
 1. If all the above is equal, password entries are sorted alphabetically.
 
+### OpenID authentication
+
+OpenID is often used when someone doesn't trust (or doesn't want to need to trust) a website with their authentication credentials. For this reason, to prevent leaking credentials Browserpass considers OpenID and username+password authentications mutually exclusive: when `openid:` field is present in a password entry, Browserpass will _only_ attempt to fill the OpenID field in a form, it will not even attempt to fill username and password fields, even if they are also present in the password entry, even if a website contains username and password fields in a login form.
+
 ### Modal HTTP authentication
 
 Due to the way browsers are implemented, browser extensions are only able to fill modal credentials (e.g. a popup for basic HTTP auth) for a website if the website in question has been opened by the extension. For this reason alone Browserpass contains functionality to open a URL associated with a password entry in the current or a new browser tab. However, please note that Browserpass is not intended as a bookmark manager.