For passwords, you can use 1password or another password manager--that's pretty much solved at this point.

Secrets that are needed in server or development contexts are a lot trickier. There's a fundamental tension between making them widely and easily available (which makes development and ops easier), and restricting access (which is necessary for security). You'll also probably have multiple versions of the same secrets in different environments, have teams of developers that all need to stay in sync, etc. etc. Password management, as important as it is, has fewer moving pieces.