unhardcode the certificate serial number

main.fnl

@@ -6,6 +6,20 @@
 (local csr (require :openssl.x509.csr))
 (local x509 (require :openssl.x509))
 (local pkey (require :openssl.pkey))
+(local bignum (require :openssl.bignum))
+
+(fn string->bignum [bytes]
+  (bignum.new
+   (string.format
+    "0x%03x%03x%03x%03x%03x"
+    (string.unpack "I4I4I4I4I4" bytes))))
+
+(fn make-serial []
+  ;; 20 bytes, but luaossl expects it as a bignum
+  (let [bytes (with-open [f (io.open "/dev/urandom" :r)]
+                (f:read 20))]
+    (string->bignum bytes)))
+
 
 (fn not-found [out]
   (doto (headers.new)
@@ -24,7 +38,7 @@
   (let [crt
         (doto (x509.new)
           (: :setVersion 2)
-          (: :setSerial 42)
+          (: :setSerial (make-serial))
           (: :setIssuer (ca-crt:getSubject))
           (: :setLifetime (os.time) (+ (* 365 86400) (os.time)))
           (: :setSubject (csr:getSubject))