This sounds rather like New Folks' Home, a short story by Clifford Simak that was first published in Analog in July 1963.
The central character is Frederick Gray, a recently retired law professor. According to the cover blurb of the Simak anthology New Folks' Home: And Other Stories:
Frederick Gray is closing in on seventy and has outlived his
usefulness as a professor of law. He has no family; his best friend,
fellow faculty member Ben Lovell, has recently died. Before Gray moves
into a retirement home, he takes a final canoe trip to a favorite
fishing spot he and Lovell had visited many times, only to find that
someone has built a house on the remote riverside. When an accident
leaves Gray stranded and in pain, he returns to the shelter seeking
aid and instead finds a new reason for living.
The "new reason" for living is to "provide certain little services", that is, to act as a consultant on questions of interstellar law. The mysterious house that has appeared has been provided for his use by the extraterrestrials. The story concludes with the lines:
Picking up the file, he went into the study and laid it on the desk.
He pulled out a drawer and took out pad and pencils and ranged them
neatly, close at hand.
He sat down and entered upon the practice of interstellar law.
The story can be read in the Analog issue held by the Luminist archive.