Add new authenticate command.
Add new authenticate command.

CryptocurrencyCabal/htcd,ppcsuite/ppcd,aakselrod/btcd,jrick/btcd,toddfries/btcd,adiabat/btcd,BitGo/prova,jrick/dcrd,glv2/ppcd,qchain/btcd,jcmincke/dcrd,DanielKrawisz/btcd,jongillham/btcd,tb00/btcd,Cleawing/btcd,dan-da/btcd,jcmincke/dcrd,wallclockbuilder/btcd,runeaune/btcd,danoctavian/btcd,Dirbaio/btcd,jcmincke/dcrd,soapboxsys/ombfullnode,soapboxsys/ombfullnode,cqswxj2013/btcd,Cleawing/btcd,jimmysong/btcd,decred/dcrd,Stash-Crypto/btcd,Roasbeef/btcd,pkothbauer/btcd,Dirbaio/btcd,stevenroose/btcd,jrick/btcd,tb00/btcd,1d4Nf6/btcd,adiabat/btcd,pkothbauer/btcd,hectorj/btcd,dajohi/btcd,jongillham/btcd,mathiasrw/btcd,Dirbaio/btcd,davecgh/btcd,btcsuite/btcd,ppcsuite/ppcd-old,btcsuitereleases/btcd,hectorj/btcd,decred/dcrd,ppcsuite/ppcd,dajohi/btcd,cjepson/btcd,Roasbeef/btcd,Stash-Crypto/btcd,davecgh/btcd,jimmysong/btcd,dajohi/btcd,CryptocurrencyCabal/htcd,runeaune/btcd,ltcsuite/ltcd,dan-da/btcd,ltcsuite/ltcd,aakselrod/btcd,glv2/ppcd,BitGo/prova,DanielKrawisz/btcd,stevenroose/btcd,ppcsuite/ppcd-old,toddfries/btcd,jrick/btcd,cqswxj2013/btcd,FactomProject/btcws,btcsuitereleases/btcd,danoctavian/btcd,btcsuite/btcd,jrick/dcrd,1d4Nf6/btcd,qchain/btcd,mathiasrw/btcd,wallclockbuilder/btcd,cjepson/btcd