dio and login functions

lib/utils/const.dart

@@ -0,0 +1,21 @@
+import 'dart:convert';
+
+String decodeBase64(String str) {
+  //'-', '+' 62nd char of encoding,  '_', '/' 63rd char of encoding
+  String output = str.replaceAll('-', '+').replaceAll('_', '/');
+  switch (output.length % 4) {
+  // Pad with trailing '='
+    case 0: // No pad chars in this case
+      break;
+    case 2: // Two pad chars
+      output += '==';
+      break;
+    case 3: // One pad char
+      output += '=';
+      break;
+    default:
+      throw Exception('Illegal base64url string!"');
+  }
+
+  return utf8.decode(base64Url.decode(output));
+}