Add JSalmon signing library for Zot6. See https://macgirvin.com/wiki/mike/Zot%2BVI/Encryption/Signatures

Zotlabs/Lib/JSalmon.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace Zotlabs\Lib;
+
+
+class JSalmon {
+
+	static function sign($data,$key_id,$key) {
+
+		$arr       = $data;
+		$data      = json_encode($data,JSON_UNESCAPED_SLASHES);
+		$data      = base64url_encode($data, false); // do not strip padding
+		$data_type = 'application/x-zot+json';
+		$encoding  = 'base64url';
+		$algorithm = 'RSA-SHA256';
+
+		$data = preg_replace('/\s+/','',$data);
+
+		// precomputed base64url encoding of data_type, encoding, algorithm concatenated with periods
+
+		$precomputed = '.' . base64url_encode($data_type,false) . '.YmFzZTY0dXJs.UlNBLVNIQTI1Ng==';
+
+		$signature  = base64url_encode(rsa_sign($data . $precomputed, $key), false);
+
+		return ([
+			'signed'    => true,
+			'data'      => $data,
+			'data_type' => $data_type,
+			'encoding'  => $encoding,
+			'alg'       => $algorithm,
+			'sigs'      => [
+				'value'  => $signature
+				'key_id' => base64url_encode($key_id)
+			]
+		]);
+
+	}
+}