Animate position of inner shadow - ios

Question

I want to animate the position of an inner shadow on a bezier I created using PaintCode. The offset of the shadow will be animated, here's two examples:
How can I make this an animatable property so that I can animate the movement of the shadow? The generated code (pasted into drawRect) looks like this:
//// General Declarations
CGContextRef context = UIGraphicsGetCurrentContext();
//// Color Declarations
UIColor* fillColor = [UIColor colorWithRed: 1 green: 1 blue: 1 alpha: 1];
UIColor* strokeColor = [UIColor colorWithRed: 0 green: 0 blue: 0 alpha: 0.508];
//// Shadow Declarations
UIColor* shadow = strokeColor;
CGSize shadowOffset = CGSizeMake(3.1, 3.1);
CGFloat shadowBlurRadius = 5;
//// Oval Drawing
UIBezierPath* ovalPath = [UIBezierPath bezierPathWithOvalInRect: CGRectMake(31.5, 33.5, 26, 26)];
[fillColor setFill];
[ovalPath fill];
////// Oval Inner Shadow
CGRect ovalBorderRect = CGRectInset([ovalPath bounds], -shadowBlurRadius, -shadowBlurRadius);
ovalBorderRect = CGRectOffset(ovalBorderRect, -shadowOffset.width, -shadowOffset.height);
ovalBorderRect = CGRectInset(CGRectUnion(ovalBorderRect, [ovalPath bounds]), -1, -1);
UIBezierPath* ovalNegativePath = [UIBezierPath bezierPathWithRect: ovalBorderRect];
[ovalNegativePath appendPath: ovalPath];
ovalNegativePath.usesEvenOddFillRule = YES;
CGContextSaveGState(context);
{
CGFloat xOffset = shadowOffset.width + round(ovalBorderRect.size.width);
CGFloat yOffset = shadowOffset.height;
CGContextSetShadowWithColor(context,
CGSizeMake(xOffset + copysign(0.1, xOffset), yOffset + copysign(0.1, yOffset)),
shadowBlurRadius,
shadow.CGColor);
[ovalPath addClip];
CGAffineTransform transform = CGAffineTransformMakeTranslation(-round(ovalBorderRect.size.width), 0);
[ovalNegativePath applyTransform: transform];
[[UIColor grayColor] setFill];
[ovalNegativePath fill];
}
CGContextRestoreGState(context);
[strokeColor setStroke];
ovalPath.lineWidth = 1;
[ovalPath stroke];