  Supersymmetry transformations change the Lagrangian $\mathscr{L}$ into a
total derivative $\delta \mathscr{L} = \partial_\mu \mathcal{V}^{\mu}$. On
manifolds with boundaries the total derivative term is an obstruction to
preserving supersymmetry. Such total derivative terms can be canceled by a
boundary action without specifying boundary conditions, but only for a
subalgebra of supersymmetry. We study compensating boundary actions for
$\mathcal{N}=1$ supersymmetry in 4d, and show that they are determined
independently of the details of the theory and of the boundary conditions. Two
distinct classes of boundary actions exist, which correspond to preserving
either a linear combination of supercharges of opposite chirality (called
A-type) or supercharges of opposite chirality independently (B-type). The first
option preserves a subalgebra isomorphic to $\mathcal{N} = 1$ in 3d, while the
second preserves only a 2d subgroup of the Lorentz symmetry and a subalgebra
isomorphic to $\mathcal{N} = (0,2)$ in 2d. These subalgebras are in one to one
correspondence with half-BPS objects: the A-type corresponds to domain walls
while the B-type corresponds to strings. We show that integrating the full
current algebra and taking into account boundary contributions leads to an
energy-momentum tensor which contains the boundary terms. The boundary terms
come from the domain wall and string currents in the two respective cases.
