authentication: use hidden form instead of referer
This also gives us some CSRF protection. Note that we make use of the hmac to protect the redirect value. Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
This commit is contained in:
Jason A. Donenfeld
22
cgit.c
22
cgit.c
@@ -614,22 +614,19 @@ static inline void open_auth_filter(struct cgit_context *ctx, const char *functi
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ctx->qry.url ? ctx->qry.url : "");
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}
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/* We intentionally keep this rather small, instead of looping and
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* feeding it to the filter a couple bytes at a time. This way, the
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* filter itself does not need to handle any denial of service or
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* buffer bloat issues. If this winds up being too small, people
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* will complain on the mailing list, and we'll increase it as needed. */
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#define MAX_AUTHENTICATION_POST_BYTES 4096
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/* The filter is expected to spit out "Status: " and all headers. */
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static inline void authenticate_post(struct cgit_context *ctx)
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{
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if (ctx->env.http_referer && strlen(ctx->env.http_referer) > 0) {
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html("Status: 302 Redirect\n");
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html("Cache-Control: no-cache, no-store\n");
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htmlf("Location: %s\n", ctx->env.http_referer);
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} else {
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html("Status: 501 Missing Referer\n");
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html("Cache-Control: no-cache, no-store\n\n");
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exit(0);
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}
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open_auth_filter(ctx, "authenticate-post");
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char buffer[MAX_AUTHENTICATION_POST_BYTES];
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int len;
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open_auth_filter(ctx, "authenticate-post");
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len = ctx->env.content_length;
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if (len > MAX_AUTHENTICATION_POST_BYTES)
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len = MAX_AUTHENTICATION_POST_BYTES;
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@@ -637,10 +634,7 @@ static inline void authenticate_post(struct cgit_context *ctx)
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die_errno("Could not read POST from stdin");
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if (write(STDOUT_FILENO, buffer, len) < 0)
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die_errno("Could not write POST to stdout");
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/* The filter may now spit out a Set-Cookie: ... */
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cgit_close_filter(ctx->cfg.auth_filter);
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html("\n");
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exit(0);
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}
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@@ -662,7 +662,8 @@ auth filter::
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the http cookie and return a 0 if it is invalid or 1 if it is invalid,
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in the exit code / close function. If the filter action is
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"authenticate-post", this filter receives POST'd parameters on
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standard input, and should write to output one or more "Set-Cookie"
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standard input, and should write a complete CGI request, preferably
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with a 302 redirect, and write to output one or more "Set-Cookie"
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HTTP headers, each followed by a newline.
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Please see `filters/simple-authentication.lua` for a clear example
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@@ -33,15 +33,28 @@ local secret = "BE SURE TO CUSTOMIZE THIS STRING TO SOMETHING BIG AND RANDOM"
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--
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--
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-- Sets HTTP cookie headers based on post
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-- Sets HTTP cookie headers based on post and sets up redirection.
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function authenticate_post()
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local password = users[post["username"]]
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-- TODO: Implement time invariant string comparison function to mitigate against timing attack.
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if password == nil or password ~= post["password"] then
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construct_cookie("", "cgitauth")
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else
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construct_cookie(post["username"], "cgitauth")
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local redirect = validate_value(post["redirect"])
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if redirect == nil then
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not_found()
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return 0
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end
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redirect_to(redirect)
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-- TODO: Implement time invariant string comparison function to mitigate timing attack.
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if password == nil or password ~= post["password"] then
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set_cookie("cgitauth", "")
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else
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-- One week expiration time
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local username = secure_value(post["username"], os.time() + 604800)
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set_cookie("cgitauth", username)
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end
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html("\n")
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return 0
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end
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@@ -54,8 +67,8 @@ function authenticate_cookie()
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return 1
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end
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local username = validate_cookie(get_cookie(http["cookie"], "cgitauth"))
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if username == nil or not accepted_users[username] then
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local username = validate_value(get_cookie(http["cookie"], "cgitauth"))
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if username == nil or not accepted_users[username:lower()] then
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return 0
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else
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return 1
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@@ -68,6 +81,9 @@ function body()
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html("<form method='post' action='")
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html_attr(cgit["login"])
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html("'>")
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html("<input type='hidden' name='redirect' value='")
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html_attr(secure_value(cgit["url"], 0))
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html("' />")
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html("<table>")
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html("<tr><td><label for='username'>Username:</label></td><td><input id='username' name='username' autofocus /></td></tr>")
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html("<tr><td><label for='password'>Password:</label></td><td><input id='password' name='password' type='password' /></td></tr>")
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@@ -78,81 +94,10 @@ function body()
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end
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--
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--
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-- Cookie construction and validation helpers.
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--
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--
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local crypto = require("crypto")
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-- Returns username of cookie if cookie is valid. Otherwise returns nil.
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function validate_cookie(cookie)
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local i = 0
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local username = ""
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local expiration = 0
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local salt = ""
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local hmac = ""
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if cookie:len() < 3 or cookie:sub(1, 1) == "|" then
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return nil
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end
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for component in string.gmatch(cookie, "[^|]+") do
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if i == 0 then
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username = component
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elseif i == 1 then
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expiration = tonumber(component)
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if expiration == nil then
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expiration = 0
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end
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elseif i == 2 then
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salt = component
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elseif i == 3 then
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hmac = component
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else
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break
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end
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i = i + 1
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end
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if hmac == nil or hmac:len() == 0 then
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return nil
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end
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-- TODO: implement time invariant comparison to prevent against timing attack.
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if hmac ~= crypto.hmac.digest("sha1", username .. "|" .. tostring(expiration) .. "|" .. salt, secret) then
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return nil
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end
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if expiration <= os.time() then
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return nil
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end
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return username:lower()
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end
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function construct_cookie(username, cookie)
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local authstr = ""
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if username:len() > 0 then
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-- One week expiration time
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local expiration = os.time() + 604800
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local salt = crypto.hex(crypto.rand.bytes(16))
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authstr = username .. "|" .. tostring(expiration) .. "|" .. salt
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authstr = authstr .. "|" .. crypto.hmac.digest("sha1", authstr, secret)
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end
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html("Set-Cookie: " .. cookie .. "=" .. authstr .. "; HttpOnly")
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if http["https"] == "yes" or http["https"] == "on" or http["https"] == "1" then
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html("; secure")
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end
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html("\n")
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end
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--
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--
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-- Wrapper around filter API follows below, exposing the http table, the cgit table, and the post table to the above functions.
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-- Wrapper around filter API, exposing the http table, the cgit table, and the post table to the above functions.
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--
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--
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@@ -197,7 +142,7 @@ end
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--
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--
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-- Utility functions follow below, based on keplerproject/wsapi.
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-- Utility functions based on keplerproject/wsapi.
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--
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--
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@@ -211,6 +156,16 @@ function url_decode(str)
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return str
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end
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function url_encode(str)
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if not str then
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return ""
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end
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str = string.gsub(str, "\n", "\r\n")
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str = string.gsub(str, "([^%w ])", function (c) return string.format("%%%02X", string.byte(c)) end)
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str = string.gsub(str, " ", "+")
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return str
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end
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function parse_qs(qs)
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local tab = {}
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for key, val in string.gmatch(qs, "([^&=]+)=([^&=]*)&?") do
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@@ -223,3 +178,90 @@ function get_cookie(cookies, name)
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cookies = string.gsub(";" .. cookies .. ";", "%s*;%s*", ";")
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return url_decode(string.match(cookies, ";" .. name .. "=(.-);"))
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end
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--
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--
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-- Cookie construction and validation helpers.
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--
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--
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local crypto = require("crypto")
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-- Returns value of cookie if cookie is valid. Otherwise returns nil.
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function validate_value(cookie)
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local i = 0
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local value = ""
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local expiration = 0
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local salt = ""
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local hmac = ""
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if cookie == nil or cookie:len() < 3 or cookie:sub(1, 1) == "|" then
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return nil
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end
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for component in string.gmatch(cookie, "[^|]+") do
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if i == 0 then
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value = component
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elseif i == 1 then
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expiration = tonumber(component)
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if expiration == nil then
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expiration = 0
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end
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elseif i == 2 then
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salt = component
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elseif i == 3 then
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hmac = component
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else
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break
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end
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i = i + 1
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end
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if hmac == nil or hmac:len() == 0 then
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return nil
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end
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-- TODO: implement time invariant comparison to prevent against timing attack.
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if hmac ~= crypto.hmac.digest("sha1", value .. "|" .. tostring(expiration) .. "|" .. salt, secret) then
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return nil
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end
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if expiration ~= 0 and expiration <= os.time() then
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return nil
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end
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return url_decode(value)
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end
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function secure_value(value, expiration)
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if value == nil or value:len() <= 0 then
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return ""
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end
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local authstr = ""
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local salt = crypto.hex(crypto.rand.bytes(16))
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value = url_encode(value)
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authstr = value .. "|" .. tostring(expiration) .. "|" .. salt
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authstr = authstr .. "|" .. crypto.hmac.digest("sha1", authstr, secret)
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return authstr
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end
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function set_cookie(cookie, value)
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html("Set-Cookie: " .. cookie .. "=" .. value .. "; HttpOnly")
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if http["https"] == "yes" or http["https"] == "on" or http["https"] == "1" then
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html("; secure")
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end
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html("\n")
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end
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function redirect_to(url)
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html("Status: 302 Redirect\n")
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html("Cache-Control: no-cache, no-store\n")
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html("Location: " .. url .. "\n")
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end
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function not_found()
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html("Status: 404 Not Found\n")
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html("Cache-Control: no-cache, no-store\n\n")
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end
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