Illegal base64 character 5f when decoding token with username with umlaut

Calling Token.getClaims(“x.eyJzdWIiOiJmb2_DpCJ9.x“) should return this JSON:

Actual result:

Cause:

Correct code:

JWT uses base64url encoding and not base64 encoding that makes a difference for umlauts and other UTF8 characters:
https://www.rfc-editor.org/rfc/rfc7519 – JWT
https://www.rfc-editor.org/rfc/rfc4648#section-5 – base64url encoding and decoding
https://www.rfc-editor.org/rfc/rfc4648#section-4 – base64 encoding and decoding