It's true that photographing portraits on an overcast day, or in a shaded area, is often preferable as you've no hard shadows to contend with, but shooting into the sun can make more creative images. It's tricky though: your camera's automatic metering system is likely to underexpose your subject and, love it or hate it, you may get flare. Using Spot metering on your subject's face or from a midtone (like grass or concrete) will ensure the camera doesn't expose for the background, a lens hood will help reduce flare and a silver or gold reflector will bounce light back on to your subject's face.
I love shooting into the sun to get rim lighting (the glow around the edges of your subject) and, occasionally, even flare but I treat the images differently depending on the time of day. A low, soft evening sun provides a glorious warm backlight that should nearly always be kept in colour to retain its signature glow, but if the light is hard and high consider turning them black & white to make the most of the strong contrast. Go on, give it ago tomorrow and see what you get!
Top tip: How to avoid flare
If you don't want flare in your shot, try one or all these tricks:
Use your lens hood
Block the sun with your hand
Position your subject in front of the sun
Angle yourself so the sun is hidden by trees or a building