@jesta u should know about @steemshot method of mapping user made password to a posting key once during registration for his steemshot app! u should check it out
steepshot60 · 3 months ago
Posting keys still confuse a lot of people, so we've decided to let the user map a normal password to a posting key once during the registration and then use this password for further logins.

However, this process will probably change in newer versions when Steem Login and Signing Service for Third-Party Applications is released in Q3 (according to the Steemit Roadmap 2017)