D-Link Dir-846 pppoe username

I a brought a DIR-846 and the ISP uses PPPOE authentication to connect. but the username field support only 32 characters. i ran a binwalk to make reverse engineering and i got this:

5928          0x1728          Copyright string: "Copyright (C) 2011 Gabor Juhos <juhosg@openwrt.org>"
6156          0x180C          LZMA compressed data, properties: 0x6D, dictionary size: 8388608 bytes, uncompressed size: 3126732 bytes
1642496       0x191000        Squashfs filesystem, little endian, version 4.0, compression:xz, size: 7788096 bytes, 1862 inodes, blocksize: 262144 bytes, created: 2019-10-15 08:29:20

I think that the router is running openwrt, can anyone helpme to solve the problem with this limitation about characters on Username of PPPOE?