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-rw-r--r--util/jwt.lua51
1 files changed, 51 insertions, 0 deletions
diff --git a/util/jwt.lua b/util/jwt.lua
new file mode 100644
index 00000000..bf106dfa
--- /dev/null
+++ b/util/jwt.lua
@@ -0,0 +1,51 @@
+local s_gsub = string.gsub;
+local json = require "util.json";
+local hashes = require "util.hashes";
+local base64_encode = require "util.encodings".base64.encode;
+local base64_decode = require "util.encodings".base64.decode;
+local secure_equals = require "util.hashes".equals;
+
+local b64url_rep = { ["+"] = "-", ["/"] = "_", ["="] = "", ["-"] = "+", ["_"] = "/" };
+local function b64url(data)
+ return (s_gsub(base64_encode(data), "[+/=]", b64url_rep));
+end
+local function unb64url(data)
+ return base64_decode(s_gsub(data, "[-_]", b64url_rep).."==");
+end
+
+local static_header = b64url('{"alg":"HS256","typ":"JWT"}') .. '.';
+
+local function sign(key, payload)
+ local encoded_payload = json.encode(payload);
+ local signed = static_header .. b64url(encoded_payload);
+ local signature = hashes.hmac_sha256(key, signed);
+ return signed .. "." .. b64url(signature);
+end
+
+local jwt_pattern = "^(([A-Za-z0-9-_]+)%.([A-Za-z0-9-_]+))%.([A-Za-z0-9-_]+)$"
+local function verify(key, blob)
+ local signed, bheader, bpayload, signature = string.match(blob, jwt_pattern);
+ if not signed then
+ return nil, "invalid-encoding";
+ end
+ local header = json.decode(unb64url(bheader));
+ if not header or type(header) ~= "table" then
+ return nil, "invalid-header";
+ elseif header.alg ~= "HS256" then
+ return nil, "unsupported-algorithm";
+ end
+ if not secure_equals(b64url(hashes.hmac_sha256(key, signed)), signature) then
+ return false, "signature-mismatch";
+ end
+ local payload, err = json.decode(unb64url(bpayload));
+ if err ~= nil then
+ return nil, "json-decode-error";
+ end
+ return true, payload;
+end
+
+return {
+ sign = sign;
+ verify = verify;
+};
+