code: public static String retrieveMasterToken(String tokenSigningKey) {
          Map<String, Object> claims = new HashMap<>();
  
          claims.put("*", String.valueOf(READ_UPDATE));
  
          return Jwts.builder()
                     .setSubject("segmentstoreresource")
                     .setAudience("segmentstore")
                     .setClaims(claims)
                     .signWith(SignatureAlgorithm.HS512, tokenSigningKey.getBytes())
                     .compact();
      }
docs: Retrieves a master token for internal controller to segmentstore communication.
  @param tokenSigningKey Signing key for the JWT token.
  @return A new master token which has highest privileges.