Support an Alternative Provider for Accessible CAPTCHA implementations


Since CAPTCHA image challenges are not highly accessible to users with disabilities, support an "alternative" provider mechanism that provides accessibility-friendly implementations that can be plugged in much like how image, filter and text providers can be plugged in now.
The provider implementation should be designed to handle a wide range of implementations, such as Q&A and audio-based CAPTCHA.
The AIP web control should be extended to support an "alternative" hyperlink, hidden by default, with a public boolean property that can be set to make it visible. When visible, the default template should show the hyperlink either above or below the image or text box (perhaps configurable via another property on the AIP web control). Developers of custom AIP web control templates should be able to add a control with an appropriate type and ID value for the hyperlink in much the same way as the image, text box and validators can be added now.
Original discussion: