I have a project requirement that says "Blockchain to validate internal app account". But the project has nothing with cryptocurrency. It's more like a linked in, social media for business. I understand nothing about blockchain. I just know that it's a virtual currency using cryptography to validate transactions. But can it be used to validate some things like account though? If it can, can you give me a hint about what to look in blockchain about validating account with blockchain? Thanks.
Blockchain is actually not cryptocurrency. That's like saying Mysql is Facebook. It's rather that Facebook uses Mysql as it's database and cryptocurrencies use blockchain as their databases.
There are several ways blockchains can be used as source of validation:
Using wallet address as "identity"
A blockchain "wallet" is actually just a number, an integer. But it's a very large one. The address is derived from the user's public key. This is the same system that is used by SSL/TLS (HTTPS) to secure websites.
What you can do is let the user register with your system with his blockchain wallet address (for example Bitcoin wallet or Etheruem wallet). To authenticate the user just have the user sign a piece of data known to you (it could be as simple as the string "Hello"). Then using his wallet address you can verify that he is who he says he is because you've proven that he has the private key needed to sign the data. In some ways this is similar to how JWT (JSON Web Token) works but JWT does not use a blockchain.
Using a smart contract
Some blockchain platforms such as Ethereum implement a feature known as "Smart Contracts". A smart contract is just a fancy name in the blockchain world for a Class that is stored in the blockchain and can interact with the blockchain. Some blockchain platforms such as Corda only allow you to store data in smart contracts and some limited validation logic. Others like Ethereum actually implement Turing-complete smart contracts that allow you to implement any logic.
You can implement your user data in smart contracts. Then the users will have to call the authentication method in the smart contract using his wallet address. All the regular security mechanisms protecting blockchain transactions are involved so the smart contract has access to the user's identity (address) and users cannot fake a transaction by using another user's address because he does not have other people's private keys. Using this you can implement authentication logic in smart contracts.