I've multiple applications running in sub-domains, under a parent-domain that I have no control of. They all require a login, which works by sending to an API request that I also have no control of.
The downside of this is that they all require login if you jump from one to another. A solution for a "single sign on" is to make a portal site that require a login once, where you then can access all these applications from there. Still, you can't jump from one to another without login, but at least you can do so by the portal-site.
The idea:
1) Encrypt your id and password upon login that will be stored in cookie in the portal-site.
2) Once visiting other page, the encrypted id + password will be sent over to the url, and then in the visited application, send the encrypted value to the backend (via my own created API) to be decrypted..
3) Once decrypted in the backend, an API request will be called for login (instead doing it on front-end as they currently does).
In other word, I will create a backend server, making a new API request to recieve the encrypted value, decrypt, and then use the actuall API request for login (that I have no control of).
Does this work, or is this againt GDPR? Is this far fetched, is there a better method?
( I'm not very experienced with this area )