Provide authentication

[timoKroecker]

User story

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At the beginning of every browser session, the user needs to authenticate himself. With a username and password he proves, who he claims to be.

Acceptance Criteria

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• Username and password are fetched after user hits enter
• Password gets hashed and compared to the hashed password in the database
• If username doesn't exist or password is incorrect, we should be redirected to the login page with error message
• If username exists and password is correct, we should be redirected to the connector UI
• The connector UI should not be accessible via the URL only (meaning without authentication)

  DoD General Criteria

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• Feature has been merged into the main branch
• Feature has been added to the documentation
• Product owner approved features
• Developers agreed to release