in port/espressif/src/base64_port.c [15:23]
int base64_port_decode( char * dst, size_t dlen, int * olen, char * src, size_t slen )
{
int rc = mbedtls_base64_decode( (unsigned char *)dst,
dlen,
(size_t *)olen,
(unsigned char *)src,
slen );
return rc == 0 ? 0 : -1;
}