Given a journal policy that authors must share original data, am I free to use this data without granting original authors authorship? There is a large database maintained by a group of scientists. This group of scientists have made a considerable effort to get many other scientists to contribute to this database, and make it available to other researchers, on the condition that to access some of the data, some data contributors may request authorship. This project has been very successful and many publications have resulted from this database. 

Recently, some authors used the entire database in an analysis, and gave associated authorship to respective authors when requested. However, this analysis is published in a journal with a specific data sharing policy that reads,

"(Journal X) requires authors to ensure that data and materials integral to the paper are available to readers in a form which allows for verification and replication of the results in the paper. Where feasible, data should be included as part of the article or as supporting information, however if this is not possible, we expect authors to make use of public data repositories and include the appropriate links and identifiers within the article. It is the strict requirement of the journal that authors will agree to make their data and materials available to readers upon reasonable request, and corresponding authors will be reminded of this at acceptance stage. Please note that this policy also applies to any custom software described in the paper."

To me, this means that if I request this data, then the original authors can no longer require me to include them as authors in any subsequent analysis I generate and choose to publish. However, it only says they have to share the data with me. It says nothing about how I am allowed to use said shared data.

Question: if I request this data, am I somehow obligated to offer authorship to the original data generators?
I'm not a fan of "mandatory authorship" on published information: I feel that once something is published, one should collect one's rewards by means of citation rather than by strong-arming people into giving you an authorship.  Mandatory authorship on already-published data feels to me too much like a form of salami-slicing on a dataset.

That said, the journal's policy does not appear to say anything at all regarding authorship.  Therefore, the default position would seem to be that the authors must share the data with you (as mandated by the journal), but are also free to require authorship as "payment" for sharing.

The journal, however, may feel that this goes against the spirit of their data sharing agreement, and if so, then you may be able to obtain the data without being coerced into authorship.  I would thus recommend, like @BrianBorchers notes in the comment, that you write to the chief editor(s) and ask for a ruling.