Answer
By ASA, $\triangle CAB \cong \triangle DAB$
Work Step by Step
Angle: $\angle CAB \cong \angle DAB$
Side: Both triangles share the side $\overline{AB}$, which is between two angles which are congruent.
Angle: $\angle ABC \cong \angle ABD$
Therefore, by ASA, $\triangle CAB \cong \triangle DAB$
