It isn't, assuming Springer doesn't have contracts with author precluding it. Springer is either the copyright holder or is authorised to distribute, and they are explicitly making the works available for download. You don't need any additional permission.
Any license changes they publish are important to establish your right to make any subsequent copies, though.
there is somewhat of a difference between "purchasing something for 0.00 with appropriate distribution after creating an account at a webshop" and "torrenting a pdf"
Any license changes they publish are important to establish your right to make any subsequent copies, though.