simple-authentication.lua: tie secure cookies to field names

diff --git a/filters/simple-authentication.lua b/filters/simple-authentication.lua
index cc86b7e3d76f491e8ea40ac30320c3dc3eca4876..de34d092135d0db24b6a7057c00e3293e9fffe2c 100644 (file)
--- a/filters/simple-authentication.lua
+++ b/filters/simple-authentication.lua
@@ -46,7 +46,7 @@ local secret = "BE SURE TO CUSTOMIZE THIS STRING TO SOMETHING BIG AND RANDOM"
 -- Sets HTTP cookie headers based on post and sets up redirection.
 function authenticate_post()
        local password = users[post["username"]]
-       local redirect = validate_value(post["redirect"])
+       local redirect = validate_value("redirect", post["redirect"])
 
        if redirect == nil then
                not_found()
@@ -60,7 +60,7 @@ function authenticate_post()
                set_cookie("cgitauth", "")
        else
                -- One week expiration time
-               local username = secure_value(post["username"], os.time() + 604800)
+               local username = secure_value("username", post["username"], os.time() + 604800)
                set_cookie("cgitauth", username)
        end
 
@@ -77,7 +77,7 @@ function authenticate_cookie()
                return 1
        end
 
-       local username = validate_value(get_cookie(http["cookie"], "cgitauth"))
+       local username = validate_value("username", get_cookie(http["cookie"], "cgitauth"))
        if username == nil or not accepted_users[username:lower()] then
                return 0
        else
@@ -92,7 +92,7 @@ function body()
        html_attr(cgit["login"])
        html("'>")
        html("<input type='hidden' name='redirect' value='")
-       html_attr(secure_value(cgit["url"], 0))
+       html_attr(secure_value("redirect", cgit["url"], 0))
        html("' />")
        html("<table>")
        html("<tr><td><label for='username'>Username:</label></td><td><input id='username' name='username' autofocus /></td></tr>")
@@ -194,9 +194,10 @@ end
 local crypto = require("crypto")
 
 -- Returns value of cookie if cookie is valid. Otherwise returns nil.
-function validate_value(cookie)
+function validate_value(expected_field, cookie)
        local i = 0
        local value = ""
+       local field = ""
        local expiration = 0
        local salt = ""
        local hmac = ""
@@ -207,15 +208,17 @@ function validate_value(cookie)
 
        for component in string.gmatch(cookie, "[^|]+") do
                if i == 0 then
-                       value = component
+                       field = component
                elseif i == 1 then
+                       value = component
+               elseif i == 2 then
                        expiration = tonumber(component)
                        if expiration == nil then
-                               expiration = 0
+                               expiration = -1
                        end
-               elseif i == 2 then
-                       salt = component
                elseif i == 3 then
+                       salt = component
+               elseif i == 4 then
                        hmac = component
                else
                        break
@@ -228,18 +231,22 @@ function validate_value(cookie)
        end
 
        -- Lua hashes strings, so these comparisons are time invariant.
-       if hmac ~= crypto.hmac.digest("sha1", value .. "|" .. tostring(expiration) .. "|" .. salt, secret) then
+       if hmac ~= crypto.hmac.digest("sha1", field .. "|" .. value .. "|" .. tostring(expiration) .. "|" .. salt, secret) then
+               return nil
+       end
+
+       if expiration == -1 or (expiration ~= 0 and expiration <= os.time()) then
                return nil
        end
 
-       if expiration ~= 0 and expiration <= os.time() then
+       if url_decode(field) ~= expected_field then
                return nil
        end
 
        return url_decode(value)
 end
 
-function secure_value(value, expiration)
+function secure_value(field, value, expiration)
        if value == nil or value:len() <= 0 then
                return ""
        end
@@ -247,7 +254,8 @@ function secure_value(value, expiration)
        local authstr = ""
        local salt = crypto.hex(crypto.rand.bytes(16))
        value = url_encode(value)
-       authstr = value .. "|" .. tostring(expiration) .. "|" .. salt
+       field = url_encode(field)
+       authstr = field .. "|" .. value .. "|" .. tostring(expiration) .. "|" .. salt
        authstr = authstr .. "|" .. crypto.hmac.digest("sha1", authstr, secret)
        return authstr
 end