The **Advanced User Guide** builds on this one, uses the same concepts, and teaches you some extra features.

But you should first read the **Tutorial - User Guide** (what you are reading right now).

   * stream is longer, its extra elements will be ignored.
   *
   * <p>Note that if you are calling {@link Stream#forEach} on the resulting stream, you might want
   * to consider using {@link #forEachPair} instead of this method.
   *
   * <p><b>Performance note:</b> The resulting stream is not <a

     *
     *            k * k <= x          <  (k + 1) * (k + 1)
     * (double) (k * k) <= (double) x <= (double) ((k + 1) * (k + 1))
     *          since casting to double is nondecreasing.
     *          Note that the right-hand inequality is no longer strict.
     * Math.sqrt(k * k) <= Math.sqrt(x) <= Math.sqrt((k + 1) * (k + 1))
     *          since Math.sqrt is monotonic.

For example, if you want to read or manipulate the request body before it is processed by your application.

/// danger

This is an "advanced" feature.

If you are just starting with **FastAPI** you might want to skip this section.

///

## Use cases

Some use cases include:

	case reflect.Float32, reflect.Float64:
		return true
	default:
		return false
	}
}

// ExplainSQL generate SQL string with given parameters, the generated SQL is expected to be used in logger, execute it might introduce a SQL injection vulnerability
func ExplainSQL(sql string, numericPlaceholder *regexp.Regexp, escaper string, avars ...interface{}) string {
	var (
		convertParams func(interface{}, int)

└─────┴─────────────────────────────────┴──────────────────────────────────┴──────────┘
```

> NOTE: Canceled decommission will not make the pool active again, since we might have  potentially partial namespace on the other pools, to avoid this scenario be absolutely sure to make decommissioning a planned well thought activity. This is not to be run on a daily basis.

```

				"us-west-1",
				"s3",
				"ABCD"),
			expectedCredentials: credentialHeader{},
			expectedErrCode:     ErrInvalidRequestVersion,
		},
		// Test Case - 9.
		// Test case with right inputs. Expected to return a valid CredentialHeader.
		// "aws4_request" is the valid request version.
		{
			inputCredentialStr: generateCredentialStr(
				"Z7IXGOO6BZ0REAN1Q26I",
				sampleTimeStr,
				"us-west-1",

     *
     *            k * k <= x          <  (k + 1) * (k + 1)
     * (double) (k * k) <= (double) x <= (double) ((k + 1) * (k + 1))
     *          since casting to double is nondecreasing.
     *          Note that the right-hand inequality is no longer strict.
     * Math.sqrt(k * k) <= Math.sqrt(x) <= Math.sqrt((k + 1) * (k + 1))
     *          since Math.sqrt is monotonic.

But first, let's check some small concepts.

## In a hurry?

If you don't care about any of these terms and you just need to add security with authentication based on username and password *right now*, skip to the next chapters.

## OAuth2

OAuth2 is a specification that defines several ways to handle authentication and authorization.

It is quite an extensive specification and covers several complex use cases.

    // GWT's ConcurrentHashMap is a wrapper around HashMap, but it rejects null keys, which matches
    // the behaviour of the non-GWT implementation of newConcurrentHashSet().
    // On the other hand HashSet might be better for code size if apps aren't
    // already using Collections.newSetFromMap and ConcurrentHashMap.
    return Collections.newSetFromMap(new ConcurrentHashMap<E, Boolean>());
  }