Controlling anonymous access to Jira
Jira allows anonymous users viewing issues that have been configured to be accessible by the group "Anyone". In such a case logging in to Jira is not necessary to view for example bug issues that you want to make public for your customers' convenience.
Controlling access to BigPicture/BigGantt
As explained in this article BigPicture and BigGantt do not allow anonymous access i.e. you must be able to log into Jira in order to have access to BigPicture/BigGantt. It is dictated by security reasons.
If a user has Jira access, this user needs to have at least the lowest BigPicture/BigGantt Global user role defined in the Security configuration of the BigPicture/BigGantt plugin.
In case it is still not clear we are more than happy to answer all customer inquiries through our support channel.