R, 54 bytes

n=scan();m=diag(n)[,n:1];m[1,1]=m[n,n]=1;write(m,'',n) 

prints to stdout; reads from stdin. creates an identity matrix diag(n), flips it top to bottom [,n:1], sets the top left and bottom right to 1, and then writes to console ('') with width n.

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R, 54 42 bytes

-12 bytes thanks to Jarko Dubbeldam

n=scan();m=diag(n)[,n:1];m[1,1]=m[n,n]=1;m 

returns a matrix; reads from stdin. creates an identity matrix diag(n), flips it top to bottom [,n:1], sets the top left and bottom right to 1, and then writes to console ('') with width n.

Try it online!