In the next chapters, I'll give you more **concrete recipes** to deploy FastAPI applications.

But for now, let's check these important **conceptual ideas**. These concepts also apply to any other type of web API. 💡

## Security - HTTPS

You will see examples of this in the next chapters, about relational and NoSQL databases, security, etc.

## **FastAPI** compatibility

The simplicity of the dependency injection system makes **FastAPI** compatible with:

* all the relational databases

But once you know the basic information of **HTTPS for developers** you can easily combine and configure different tools to help you manage everything in a simple way.

* `deprecated`

Validations specific for strings:

* `min_length`
* `max_length`
* `pattern`

In these examples you saw how to declare validations for `str` values.

import java.text.ParseException
import java.text.SimpleDateFormat
import java.util.Date
import java.util.TimeZone
import kotlin.reflect.KClass
import okio.ByteString

/**
 * Built-in adapters for reading standard ASN.1 types.
 */
internal object Adapters {
  val BOOLEAN =
    BasicDerAdapter(
      name = "BOOLEAN",
      tagClass = DerHeader.TAG_CLASS_UNIVERSAL,
      tag = 1L,
      codec =

   * ```
   */
  private val attributeTypeAndValue: BasicDerAdapter<AttributeTypeAndValue> =
    Adapters.sequence(
      "AttributeTypeAndValue",
      Adapters.OBJECT_IDENTIFIER,
      Adapters.any(
        String::class to Adapters.UTF8_STRING,
        Nothing::class to Adapters.PRINTABLE_STRING,
        AnyValue::class to Adapters.ANY_VALUE,
      ),
      decompose = {
        listOf(
          it.type,

    val bytes = "020132".decodeHex()
    assertThat(Adapters.INTEGER_AS_LONG.toDer(50L)).isEqualTo(bytes)
    assertThat(Adapters.INTEGER_AS_LONG.fromDer(bytes)).isEqualTo(50L)
  }

  @Test fun `decode negative integer`() {
    val bytes = "02019c".decodeHex()
    assertThat(Adapters.INTEGER_AS_LONG.fromDer(bytes)).isEqualTo(-100L)
    assertThat(Adapters.INTEGER_AS_LONG.toDer(-100L)).isEqualTo(bytes)
  }

            <title>Script blocks</title>
            <para>No script blocks</para>
        </section>
    </chapter>
</root>'''
    }

    def rendersKnownSubtypes() {
        def sourceContent = parse('''
            <chapter>
                <section><title>Properties</title></section>
            </chapter>
        ''')

   *
   * <p><i>Notes:</i> This is an implementation of the algorithm for Lexicographical Permutations
   * Generation, described in Knuth's "The Art of Computer Programming", Volume 4, Chapter 7,
   * Section 7.2.1.2. The iteration order follows the lexicographical order. This means that the
   * first permutation will be in ascending order, and the last will be in descending order.
   *

# Simple OAuth2 with Password and Bearer

Now let's build from the previous chapter and add the missing parts to have a complete security flow.

## Get the `username` and `password`

We are going to use **FastAPI** security utilities to get the `username` and `password`.

OAuth2 specifies that when using the "password flow" (that we are using) the client/user must send a `username` and `password` fields as form data.