FOI - Petitions

I wish to submit an electronic petition to the Mayor of London that I initiated on Change.org. I notice that your guidance states that electronic petitions must include the email addresses of people who have signed in order to "validate the petition". 

Please can you answer the following questions: 

1. How does the provision of people's email addresses allow the GLA to "validate" a petition? 

2. How can you validate a person's identity through the provision of an email address? 

3. What use does the GLA intend to make of the names and email addresses provided by people who have signed the petition? 

4. What will happen to people's names and email addresses in the GLA's possession? 

5. Please can you provide the relevant legislation that shows that the Mayor of London has the right to demand a person's email address as a prerequisite for validation of a petition under data protection legislation? 

CLARIFICATION

This is the only link to petitions addressed to the Mayor that I can find on the GLA's website and is the one to which I refer in my earlier message of 19 August 2019: 

https://www.london.gov.uk/about-us/london-assembly/petitions