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

1 files changed, 21 insertions, 13 deletions

diff --git a/filters/simple-authentication.lua b/filters/simple-authentication.lua
index cc86b7e..de34d09 100644
--- 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