  We present a powerful and general approach to describe the coupling of
Majorana fermions to external leads, of interacting or non-interacting
electrons. Our picture has the Klein factors of bosonization appearing as extra
Majoranas hybridizing with the physical ones. We demonstrate the power of this
approach by solving a highly nontrivial SO(M) Kondo problem arising in
topological superconductors with M Majorana-lead couplings, allowing for
arbitrary M and for conduction electron interactions. We find that these
topological Kondo problems give rise to robust non-Fermi liquid behavior, even
for Fermi liquid leads, and to a quantum phase transition between insulating
and Kondo regimes when the leads form Luttinger liquids. In particular, for M=4
we find a long sought-after stable realization of the two-channel Kondo fixed
point.
