parse JWT expiry time

app/jwt.js

@@ -0,0 +1,21 @@
+// Get the expiration timestamp of a token in unix epoch milliseconds
+export function jwtExpiry(token) {
+  try {
+    const tokenPayloadBase64 = token.split(".")[1]; // JWT payload is the second part
+    const tokenPayload = JSON.parse(
+      Buffer.from(tokenPayloadBase64, "base64").toString()
+    );
+
+    if (tokenPayload.exp) {
+      const expTimestamp = tokenPayload.exp;
+      const expTimestampMillisecond = expTimestamp * 1000;
+      return expTimestampMillisecond;
+    }
+
+    // token does not have an expiration claim, expire immediately
+    return -1;
+  } catch (e) {
+    // token parsing failed, expire immediately
+    return -1;
+  }
+}