Password protected slideshows
For more confidentiality it would be useful to have password protected slides.

Done! You can now password protect any private presentation. More info in the help article: http://help.slides.com/knowledgebase/articles/497189
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Tony Su commented
Depending on the extent and if Github integration is implemented, then security issues like this can be wrapped around slid.es by Github.
Same could be true no matter what storage partner is selected (assuming that slid.es folks aren't into architecting your own underlying cloud platform below the web app).
Depending on what is being used for slid.es user management(Uservoice?), that might be another possibility.