%% You should probably cite rfc8823 instead of this I-D.
@techreport{ietf-acme-email-smime-05,
    number =    {draft-ietf-acme-email-smime-05},
    type =      {Internet-Draft},
    institution =   {Internet Engineering Task Force},
    publisher = {Internet Engineering Task Force},
    note =      {Work in Progress},
    url =       {https://datatracker.ietf.org/doc/draft-ietf-acme-email-smime/05/},
    author =    {Alexey Melnikov},
    title =     {{Extensions to Automatic Certificate Management Environment for end user S/MIME certificates}},
    pagetotal = 8,
    year =      2019,
    month =     jul,
    day =       8,
    abstract =  {This document specifies identifiers and challenges required to enable the Automated Certificate Management Environment (ACME) to issue certificates for use by email users that want to use S/MIME.},
}