# Security - First Steps { #security-first-steps }

Let's imagine that you have your **backend** API in some domain.

And you have a **frontend** in another domain or in a different path of the same domain (or in a mobile application).

And you want to have a way for the frontend to authenticate with the backend, using a **username** and **password**.

We can use **OAuth2** to build that with **FastAPI**.

Sebastián Ramírez <******@****.***> 1731170360 +0100

Sebastián Ramírez <******@****.***> 1731896744 +0100

Sebastián Ramírez <******@****.***> 1731896744 +0100

Sebastián Ramírez <******@****.***> 1731896744 +0100

Sebastián Ramírez <******@****.***> 1735583217 +0000

Sebastián Ramírez <******@****.***> 1731896744 +0100

  val android5 = sslLabsClients.first { it.userAgent == "Android" && it.version == "5.0.0" }
  val android9 = sslLabsClients.first { it.userAgent == "Android" && it.version == "9.0" }
  val chrome33 = sslLabsClients.first { it.userAgent == "Chrome" && it.version == "33" }
  val chrome57 = sslLabsClients.first { it.userAgent == "Chrome" && it.version == "57" }
  val chrome80 = sslLabsClients.first { it.userAgent == "Chrome" && it.version == "80" }

     * @param first
     *            The first value
     * @param second
     *            The second value
     */
    public Pair(final T1 first, final T2 second) {
        this.first = first;
        this.second = second;
    }

    /**
     * Returns the first value.
     *
     * @return The first value
     */
    public T1 getFirst() {
        return first;
    }

    /**
     * Sets the first value.

/**
 * A tuple of three values.
 *
 * @author koichik
 * @param <T1>
 *            The type of the first value
 * @param <T2>
 *            The type of the second value
 * @param <T3>
 *            The type of the third value
 */
public class Tuple3<T1, T2, T3> {

    /** The first value */
    protected T1 value1;

    /** The second value */
    protected T2 value2;

    /** The third value */