So, yes, Google does pass PageRank from unsecured HTTP to HTTPS URLs through redirects.
A person asked on Twitter if Google passes PageRank from unsecured HTTP pages to HTTPS when proper permanent redirects exist.
Google’s Search Advocate, John Mueller, answered his question by saying that there’s no special “security dust” involved and that this is how Google does canonicalization.
Now that you know that Google does pass PageRank from unsecured HTTP to HTTPS URLs through redirects, just make sure to use a 301 redirect (not a 302 or 303) on a URL by URL basis so that the migration won’t take too long.