"Invalid JWT Signature."

[madc0w]

I am trying to submit a sitemap.xml programmatically, following instructions here:
https://developers.google.com/webmaster-tools/search-console-api-original/v3/sitemaps/submit#auth

I do:

// Just call this once to set JWT
HTTPJWT.setJWTOptions({
	email : "[ client ID up to the first dot ]@developer.gserviceaccount.com",
	key : Assets.getText("key.pem"), // Get key file from assets
	scopes : [
		"https://www.googleapis.com/auth/webmasters"
	],
});

var submitUrl = "https://www.googleapis.com/webmasters/v3/sites/https%3A%2F%2Fwww.spoticle.com/sitemaps/https%3A%2F%2Fwww.spoticle.com%2Fsitemap.xml";
var result = HTTPJWT.get(submitUrl);

... and here is the result:

Error: failed [400] { "error" : "invalid_grant", "error_description" : "Invalid JWT Signature." }

I can, however, generate a JWT by doing:

var jwt = GoogleOAuthJWT.encodeJWT({
	email : "[ client ID up to the first dot ]@developer.gserviceaccount.com",
	key : Assets.getText("key.pem"), // Get key file from assets
	scopes : [
		"https://www.googleapis.com/auth/webmasters"
	]
});

... but I don't know how to verify that this token is valid.

Any help appreciated. Thanks.