iframe in popup leaflet

[John froeschke]

I'm using leaflet with shiny and trying to add a webpage in the popup using an iframe tag.  It works fine locally but does not work on the web.  Any ideas on how to make this work.  The relevent bit of code is below:

addPolygons(data=MadisonSwanson, fillOpacity=0.5, stroke=FALSE,
            fillColor='#66c2a5',
            popup= ~ paste("<a><b>Madison and Swanson</a></b>",
                           "Seasonal area closures implemented to protect Gulf reef fish",
                           '<a href="http://sero.nmfs.noaa.gov/maps_gis_data/fisheries/gom/documents/madswan_steam_edges.txt" target="_blank">Federal regulations</a>',
                           '<iframe src="http://sero.nmfs.noaa.gov/maps_gis_data/fisheries/gom/documents/madswan_steam_edges.txt"></iframe>',
                           sep="<br/>"),
            group="Madison and Swanson")  %>%

The app can be viewed here: https://gulfcouncilportal.shinyapps.io/reeffishmanagementareas.  Ideally, the page here: http://sero.nmfs.noaa.gov/maps_gis_data/fisheries/gom/documents/madswan_steam_edges.txt would display in the popup using something like this 

 '<iframe src="http://sero.nmfs.noaa.gov/maps_gis_data/fisheries/gom/documents/madswan_steam_edges.txt"></iframe>'

Any help greatly appreciated.

[John froeschke]

Quick update.  I downloaded the files locally to the www folder and the popups work using the iframe tag.

 '<iframe src="madswan_steam_edges.txt"></iframe>'