On the process of submission of a paper to a journal, we have to show the referee our nucleotide sequence submitted as "Hold-Until-Published" status...

DDBJ does not provide any procedure for a limited disclosure by the password authentication or else.
When you have to show your sequence data submitted with “Hold-Until-Published” status for only particular individuals, you can send as a text file including your sequences to them.
If the referee wish to confirm the condition and/or the descriptions of your sequence submission, you can choose either of the following two procedures;

a) Publish your sequences through DDBJ.: If you do not mind to open your sequences to the public, please send us your request to publicize your submitted sequences with all of accession numbers.
b) Send DDBJ flat files of your submission to the referee, directly: When the submitter requests to us, we send the text file including DDBJ flat files to the submitter. So, please send us your request with all of accession numbers to get DDBJ flat file(s) of your submission. Then, you can forward the text file to the referee.