Kasner metric tensor

I have some questions about the Kasner spacetime. Proper distance $ds^2$ can be derived from equation: $$ds^2=dt^2-sum^3_{i=1}a^2_{i}(t)(dx^i)^2$$ The metric tensor in FRW spacetime can be written basis-free as a matrix: $$g_{munu}=begin{bmatrix}
-1 & 0 & 0 & 0
0 & a^2(t) & 0 & 0
0 & 0 & a^2(t) & 0
0 & 0 & 0 & a^2(t)
end{bmatrix}$$

Question: how do I determine the FRW metric tensor for Kasner spacetime? I did not find this on the net.

EDIT

I read a little more about Kasner metric. In the article "The Exact Vacuum Solution for Kasner Metric from
Bianchi Type-I Cosmological Model" it states that if $H_1=H_2=H_3=0$, the metric of Kasner space turns into the Minkowski metric. So, if $a_1neq const$, $a_2neq const$, $a_3neq const$, metric tensor of the Kasner space looks like this?:
$$g_{munu}=begin{bmatrix}
-1 & 0 & 0 & 0
0 & a_1^2(t) & 0 & 0
0 & 0 & a_2^2(t) & 0
0 & 0 & 0 & a_3^2(t)
end{bmatrix}$$
I’ll be grateful to hear any response.