What's the value of $a$ ?

Let the $x$ and $y$ intercepts be $x_0$ and $y_0$ respectively. Then we have:

$\begin{cases} x_0 \tan a = 1 & \implies x_0 = \frac {\cos a}{\sin a} \\ y_0 \sec a = 1 & y_0 = \cos a \end{cases}$

$\begin{aligned} \implies x_0y_0 & = \sin a \\ \frac {\cos a}{\sin a} \cdot \cos a & = \sin a \\ \cos^2 a & = \sin ^2 a \\ \implies \cos a & = \sin a \\ \implies a & = \boxed{45}^\circ \end{aligned}$