Cross-domain proof-of-possession

A computer system, comprising:

• one or more servers that, at least:
• receive from a web browser a first access request associated with a first domain, the first access request associated with an access token, the access token being associated with a map of key-value pairs with each key-value pair corresponding to a domain in a plurality of domains;
• receive from the web browser a second access request associated with a second domain, the second access request associated with the access token,
• redirect the second access request to cause the web browser to request, from the first domain, a registration of the second domain with the access token;
• and
• grant the second access request based at least in part on the registration of the second domain.

A computer-implemented method, comprising:

• receiving a first access request associated with a first domain, the first access request associated with an access token and signed with a nonce token, the access token being associated with a map of key-value pairs with each key-value pair corresponding to a domain in a plurality of domains;
• receiving a second access request associated with a second domain and signed with the nonce token, the second access request associated with the access token;
• redirecting the second access request to cause a registration request, from the first domain, for a registration of the second domain with the access token;
• adding a new key-value pair corresponding to the second domain to the map of key-value pairs such that the access token is updated for the first domain and the second domain;
• and
• granting the second access request based at least in part on the new key-value pair added in the access token.