22. (12 points) Given the function
$$
f(x)=\ln (a x+1)+\frac{1-x}{1+x}(x \geqslant 0, a>0) \text {. }
$$
(1) If $f(x)$ has an extremum at $x=1$, find the value of $a$;
(2) If $f(x) \geqslant \ln 2$ always holds, find the range of values for $a$.
22. (1) It is easy to know, $f^{\prime}(x)=\frac{a x^{2}+a-2}{(a x+1)(x+1)^{2}}$.

From $f^{\prime}(1)=0 \Rightarrow a=1$.
At this point, $f^{\prime}(x)=\frac{x^{2}-1}{(x+1)^{3}}$.
Thus, $f(x)$ is decreasing on the interval $(0,1)$ and increasing on the interval $(1,+\infty)$.
Therefore, $x=1$ is an extremum point.
(2) When $0\ln 2 \text {. }
$$

In summary, $a \geqslant 1$.