import re
s = 'https://e...content-available-to-author-only...e.com/example/page/'
print(re.sub(r'(https?|ftps?)://|/', lambda x: x.group(0) if x.group(1) else '%', s))
aW1wb3J0IHJlCnMgPSAnaHR0cHM6Ly9lLi4uY29udGVudC1hdmFpbGFibGUtdG8tYXV0aG9yLW9ubHkuLi5lLmNvbS9leGFtcGxlL3BhZ2UvJwpwcmludChyZS5zdWIocicoaHR0cHM/fGZ0cHM/KTovL3wvJywgbGFtYmRhIHg6IHguZ3JvdXAoMCkgaWYgeC5ncm91cCgxKSBlbHNlICclJywgcykpCg==