Can you post some code for solutions you've attempted so we can work from there? My initial thoughts are that you can just tweak the regex to exclude an optional trailing period. maybe something like:

while(<DATA>){
  s#(https?://\S+?)(\.?\s)#<a href="$1">$1</a>$2#igs;
  print;
}
__DATA__
Students can activate their UMSIS userids on-line by filling out and s
+ubmitting the form at https://umsis.miami.edu/sign-up.
...which can be obtained via the web at http://www.miami.edu/it-forms/
+.
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