Implement support for SameSite attribute

SameSite is an update to RFC6265, allowing servers to assert
that user agents should not send certain cookies along with
cross-site requests.

See: https://tools.ietf.org/html/draft-west-first-party-cookies-07

3 files changed, 57 insertions, 6 deletions

diff --git a/README.md b/README.md
index 5ac833d..3248285 100644
--- a/README.md
+++ b/README.md
@@ -62,7 +62,7 @@ Synopsis
                     key = "Name", value = "Bob", path = "/",
                     domain = "example.com", secure = true, httponly = true,
                     expires = "Wed, 09 Jun 2021 10:18:14 GMT", max_age = 50,
-                    extension = "a4334aebaec"
+                    samesite = "Strict", extension = "a4334aebaec"
                 })
                 if not ok then
                     ngx.log(ngx.ERR, err)
@@ -122,6 +122,7 @@ syntax: ok, err = cookie_obj:set({
     secure = true, httponly = true,
     expires = "Wed, 09 Jun 2021 10:18:14 GMT",
     max_age = 50,
+    samesite = "Strict",
     extension = "a4334aebaec"
 })
 ```
diff --git a/lib/resty/cookie.lua b/lib/resty/cookie.lua
index 11d435f..b61877e 100644
--- a/lib/resty/cookie.lua
+++ b/lib/resty/cookie.lua
@@ -8,6 +8,7 @@ local sub           = string.sub
 local format        = string.format
 local log           = ngx.log
 local ERR           = ngx.ERR
+local WARN          = ngx.WARN
 local ngx_header    = ngx.header
 
 local EQUAL         = byte("=")
@@ -136,6 +137,17 @@ local function bake(cookie)
     if cookie["max-age"] then
         cookie.max_age = cookie["max-age"]
     end
+
+    if (cookie.samesite) then
+        local samesite = cookie.samesite
+
+        -- if we dont have a valid-looking attribute, ignore the attribute
+        if (samesite ~= "Strict" and samesite ~= "Lax") then
+            log(WARN, "SameSite value must be 'Strict' or 'Lax'")
+            cookie.samesite = nil
+        end
+    end
+
     local str = cookie.key .. "=" .. cookie.value
         .. (cookie.expires and "; Expires=" .. cookie.expires or "")
         .. (cookie.max_age and "; Max-Age=" .. cookie.max_age or "")
@@ -143,6 +155,7 @@ local function bake(cookie)
         .. (cookie.path and "; Path=" .. cookie.path or "")
         .. (cookie.secure and "; Secure" or "")
         .. (cookie.httponly and "; HttpOnly" or "")
+        .. (cookie.samesite and "; SameSite=" .. cookie.samesite or "")
         .. (cookie.extension and "; " .. cookie.extension or "")
     return str
 end
diff --git a/t/sanity.t b/t/sanity.t
index 952b81e..cb52ae8 100644
--- a/t/sanity.t
+++ b/t/sanity.t
@@ -5,7 +5,7 @@ use Cwd qw(cwd);
 
 repeat_each(2);
 
-plan tests => repeat_each() * (blocks() * 3 + 4);
+plan tests => repeat_each() * (blocks() * 3 + 6);
 
 my $pwd = cwd();
 
@@ -53,8 +53,6 @@ Cookie: SID=31d4d96e407aad42; lang=en-US
 SID => 31d4d96e407aad42
 lang => en-US
 
-
-
 === TEST 2: sanity 2
 --- http_config eval: $::HttpConfig
 --- config
@@ -188,7 +186,7 @@ SID => foo
                 key = "Name", value = "Bob", path = "/",
                 domain = "example.com", secure = true, httponly = true,
                 expires = "Wed, 09 Jun 2021 10:18:14 GMT", max_age = 50,
-                extension = "a4334aebaec"
+                samesite = "Strict", extension = "a4334aebaec"
             })
             if not ok then
                 ngx.log(ngx.ERR, err)
@@ -202,7 +200,7 @@ GET /t
 --- no_error_log
 [error]
 --- response_headers
-Set-Cookie: Name=Bob; Expires=Wed, 09 Jun 2021 10:18:14 GMT; Max-Age=50; Domain=example.com; Path=/; Secure; HttpOnly; a4334aebaec
+Set-Cookie: Name=Bob; Expires=Wed, 09 Jun 2021 10:18:14 GMT; Max-Age=50; Domain=example.com; Path=/; Secure; HttpOnly; SameSite=Strict; a4334aebaec
 --- response_body
 Set cookie
 
@@ -307,3 +305,42 @@ GET /t
 --- raw_response_headers_unlike: Set-Cookie: Name=Bob; Path=/\r\nSet-Cookie: Age=20\r\nSet-Cookie: Name=Bob; Path=/
 --- response_body
 Set cookie
+
+
+=== TEST 9: set cookie with invalid SameSite attribute
+--- http_config eval: $::HttpConfig
+--- config
+    location /t {
+        content_by_lua '
+            local ck = require "resty.cookie"
+            local cookie, err = ck:new()
+            if not cookie then
+                ngx.log(ngx.ERR, err)
+                return
+            end
+
+            local ok, err = cookie:set({
+                key = "Name", value = "Bob", path = "/",
+                domain = "example.com", secure = true, httponly = true,
+                expires = "Wed, 09 Jun 2021 10:18:14 GMT", max_age = 50,
+                samesite = "blahblah", extension = "a4334aebaec"
+            })
+            if not ok then
+                ngx.log(ngx.ERR, err)
+                return
+            end
+            ngx.say("Set cookie")
+        ';
+    }
+--- request
+GET /t
+--- no_error_log
+[error]
+--- error_log
+SameSite value must be 'Strict' or 'Lax'
+--- response_headers
+Set-Cookie: Name=Bob; Expires=Wed, 09 Jun 2021 10:18:14 GMT; Max-Age=50; Domain=example.com; Path=/; Secure; HttpOnly; a4334aebaec
+--- response_body
+Set cookie
+
+