We have a web app where the user has to log in at the beginning. The login shows our company logo, the name of the product incl. logo of the product and the login form:
I showed this app to a test person. He said: "What will you do with my credentials"? How can I design a more trustwothy login form.
The trust is not built at the logi form but before! It takes into account the presentation of content, footer of your site and some associations verifying the authenticity.
Depends on business you are operating, one of the biggest trust building factor can be simple login form with links to your public domain content. Like contact details with real address. People trust address more than PO BOX number or just a email id.
Disclaimers like "We do not trade your personal details" comes in picture before login screen. It is decided at the time of registration. But providing "Need Help" link which presents, for example a comprehensive FAQ, can boost the confidence of user.
Simplicity without doubt.
It may be helpful to have a description on the bottom to help the user understand what the product is. Even if you have already explained - it helps the user confirm they are logging into the correct service.
Another idea - you could create a private policy to ensure your users feel safe.
You could ask yourself if it is required to create a login screen. If there is no need to signin (for example the functionality is not really restricted to a person or can be accessed using a public account) then forget the login screen.
If a login is really required then leave a message on the page what happens with the information. For example state that the password is encrypted and that the information is just for identification purposes.
But again: Looking at the question he/she does not understand why a login is required.
It would help if you changed your test to include a landing page with information. This page can lead to use to a signup process or an account creation. An informed user will make informed decisions.
You should ask if the brand name and product name create any untrustworth-ness to user perception. If you clarify brand or product name has not any trustworthy issue, you can try to give "reasoning" or "promises" at the context of login form.
"We won't post something to your facebook wall, we promise" - can be nice for facebook social login.
"We don't tweet for advertising" - can be nice for twitter social login.
We need your e-mail(orthodoxy) because (any sensible reason) - This can help to convince user to continue to an action.
Lastly, you can create counter-arguments like if they signed up, why don't they want to log-in? If you are using an username and password of another web application, then you shall show product or company has legal papers for to do business on top of that service.
