Add JWT Bearer Authentication support and tutorial

src/jwt.h

@@ -0,0 +1,27 @@
+#pragma once
+
+#include "arch.h"
+#include "str.h"
+#include "tls.h"
+
+struct mg_jwt_opts {
+  struct mg_str claims;  // JSON payload
+  struct mg_str header;  // Extra header members, no braces; alg/typ are set
+  struct mg_str kid;     // Key ID protected header
+  struct mg_str secret;  // HS256 secret
+  const uint8_t *private_key;  // ES256 private key (MG_TLS_BUILTIN only)
+  const uint8_t *public_key;   // ES256 public key (MG_TLS_BUILTIN only)
+};
+
+// Signs JSON claims as a compact JWT. Returns JWT length, or 0 on error.
+size_t mg_jwt_sign_hs256(const struct mg_jwt_opts *opts, char *buf,
+                         size_t len);
+
+// Verifies JWT and decodes JSON claims into buf. Returns claims length, or 0.
+size_t mg_jwt_verify_hs256(struct mg_str jwt, const struct mg_jwt_opts *opts,
+                           char *buf, size_t len);
+
+size_t mg_jwt_sign_es256(const struct mg_jwt_opts *opts, char *buf,
+                         size_t len);
+size_t mg_jwt_verify_es256(struct mg_str jwt, const struct mg_jwt_opts *opts,
+                           char *buf, size_t len);