How to get username after logged in?.I am trying with MSAL (@azure/msal-angular) for Azure Signin

You can retrieve the user from MsalService, for example with:

const accountInfo: AccountInfo | null = this.msalService.instance.getActiveAccount();

It's recommended to wait until the authentication process is complete before you invoke this. This can be done by checking MsalBroadcastService:

const account: Observable<AccountInfo | null> = this.msalBroadcastService
    .inProgress$
    .pipe(
        filter(status => status == InteractionStatus.None),
        map(() => {
            const instance: IPublicClientApplication = this.msalService.instance;
            const activeAccount: AccountInfo | null = instance.getActiveAccount();
            const accounts: AccountInfo[] = instance.getAllAccounts();
            if (activeAccount != null) return activeAccount;
            if (accounts.length > 0) {
                const [firstAccount] = accounts;
                instance.setActiveAccount(firstAccount);
                return firstAccount;
            }
            return null;
        })
    );
  
    });