For authentication purpose at any 3rd party system, the usage of JWT is quite common.
Unfortunately the regarding token field in table limetoken<SID> is limited to character varying (35).
Increase size of token field to VAR_CHAR(1024) and we can import JWT in order to authorize Limesurvey participants at any 3rd party system.
At least for PostgreSQL it's no big issue.

Obstacles expected w/ mysql:
Error: #1071 - Specified key was too long; max key length is 1000 bytes
which means, the key will become too long. Max size was VARCHAR(334).

Solution:
Take only a subset of the JWT as KEY via
KEY idx_token_token_123456 (token(72))
As first 36 char are the header, which will always be the same I've used 36+1+35 = 72 char which (header+dot+35char as we have now)

CREATE TABLE tokens_123456 (
tid int(11) NOT NULL AUTO_INCREMENT,
participant_id varchar(50) COLLATE utf8_unicode_ci DEFAULT NULL,
firstname varchar(40) COLLATE utf8_unicode_ci DEFAULT NULL,
lastname varchar(40) COLLATE utf8_unicode_ci DEFAULT NULL,
email text COLLATE utf8_unicode_ci,
emailstatus text COLLATE utf8_unicode_ci,
token varchar(1024) COLLATE utf8_unicode_ci DEFAULT NULL,
language varchar(25) COLLATE utf8_unicode_ci DEFAULT NULL,
blacklisted varchar(17) COLLATE utf8_unicode_ci DEFAULT NULL,
sent varchar(17) COLLATE utf8_unicode_ci DEFAULT 'N',
remindersent varchar(17) COLLATE utf8_unicode_ci DEFAULT 'N',
remindercount int(11) DEFAULT '0',
completed varchar(17) COLLATE utf8_unicode_ci DEFAULT 'N',
usesleft int(11) DEFAULT '1',
validfrom datetime DEFAULT NULL,
validuntil datetime DEFAULT NULL,
mpid int(11) DEFAULT NULL,
PRIMARY KEY (tid),
KEY idx_token_token_123456 (token(72))
) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;