Using .ics URLs To Cross-Subscribe Event Feeds Between Yahoo and Google Calendars

The other day I was approach by a client who wanted to connect to Yahoo calendar with their Google calendar.

Unfortunally it's not a simple as it sounds. 

The only way to share these calendars with each other is using the ICS URL file protocol, which is, regretfully, read-only.

In other words, events imported through these calendar feeds cannot be edited or removed, nor can new events be added. 

For example, let's start off with importing the Google Calendar into Yahoo.

Google calendars can be shared with, quite literally, almoast any service using the ics/ical URL:

To subscribe to this particular Google calendar in Yahoo:

 

To do the reverse, ie- share your Yahoo Calendar with your Google Account:

If you want/need bi-directional synchronization with Google calendar you need to use a protocol called CalDav. If you're not using Google apps sync on your desktop, this is how Outlook, iCal and lighting all connect to google calendar, offering bi-directional access.  

To my knowledge, & from my research, I cannot find any documentation or findings for using Google or Yahoo as an CalDav client, only as a server. 

The only work around. I could find is to create an event in one calendar and send an invite to the other. 

Other work arounds include using third-party services (everything from a smartphone to something like an Exchange Server).