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# AWS Built-in Parameters
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The `AwsBuiltIns` class provides AWS-specific built-in parameters for endpoint rules. These parameters enable AWS-aware endpoint resolution with configuration for regions, dual-stack, FIPS compliance, and service-specific settings.
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## Capabilities
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### Core AWS Parameters
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#### Region Parameter
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```java { .api }
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/**
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 * Built-in parameter representing the AWS region used to dispatch requests
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 */
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public static final Parameter REGION = Parameter.builder()
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    .name("Region")
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    .type(ParameterType.STRING)
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    .builtIn("AWS::Region")
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    .documentation("The AWS region used to dispatch the request.")
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    .build();
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```
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#### Dual Stack Parameter
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```java { .api }
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/**
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 * Built-in parameter representing the DualStack parameter for SDKs
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 */
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public static final Parameter DUALSTACK = Parameter.builder()
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    .name("UseDualStack")
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    .type(ParameterType.BOOLEAN)
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    .builtIn("AWS::UseDualStack")
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    .documentation("When true, use the dual-stack endpoint. If the configured endpoint does not support dual-stack, dispatching the request MAY return an error.")
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    .required(true)
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    .defaultValue(Value.booleanValue(false))
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    .build();
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```
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#### FIPS Parameter
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```java { .api }
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/**
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 * Built-in parameter representing whether the endpoint must be FIPS-compliant
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 */
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public static final Parameter FIPS = Parameter.builder()
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    .name("UseFIPS")
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    .type(ParameterType.BOOLEAN)
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    .builtIn("AWS::UseFIPS")
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    .documentation("When true, send this request to the FIPS-compliant regional endpoint. If the configured endpoint does not have a FIPS compliant endpoint, dispatching the request will return an error.")
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    .required(true)
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    .defaultValue(Value.booleanValue(false))
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    .build();
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```
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### Authentication Parameters
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#### Account ID Parameter
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```java { .api }
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/**
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 * Built-in parameter representing the AccountId
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 */
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public static final Parameter ACCOUNT_ID = Parameter.builder()
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    .name("AccountId")
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    .type(ParameterType.STRING)
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    .builtIn("AWS::Auth::AccountId")
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    .documentation("The AWS AccountId used for the request.")
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    .build();
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```
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#### Account ID Endpoint Mode Parameter
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```java { .api }
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/**
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 * Built-in parameter representing the AccountId Endpoint Mode
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 */
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public static final Parameter ACCOUNT_ID_ENDPOINT_MODE = Parameter.builder()
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    .name("AccountIdEndpointMode")
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    .type(ParameterType.STRING)
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    .builtIn("AWS::Auth::AccountIdEndpointMode")
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    .documentation("The AccountId Endpoint Mode.")
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    .build();
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```
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#### Credential Scope Parameter
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```java { .api }
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/**
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 * Built-in parameter representing the Credential Scope
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 */
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public static final Parameter CREDENTIAL_SCOPE = Parameter.builder()
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    .name("CredentialScope")
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    .type(ParameterType.STRING)
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    .builtIn("AWS::Auth::CredentialScope")
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    .documentation("The AWS Credential Scope used for the request.")
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    .build();
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```
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### S3-Specific Parameters
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#### S3 Accelerate Parameter
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```java { .api }
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/**
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 * S3-specific parameter for acceleration. MUST only be used by S3 rules.
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 */
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public static final Parameter S3_ACCELERATE = Parameter.builder()
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    .type(ParameterType.BOOLEAN)
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    .name("Accelerate")
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    .builtIn("AWS::S3::Accelerate")
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    .required(true)
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    .defaultValue(Value.booleanValue(false))
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    .documentation("When true, use S3 Accelerate. NOTE: Not all regions support S3 accelerate.")
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    .build();
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```
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#### S3 Disable MRAP Parameter
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```java { .api }
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/**
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 * S3-specific parameter for disabling multi-region access points. MUST only be used by S3 rules.
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 */
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public static final Parameter S3_DISABLE_MRAP = Parameter.builder()
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    .type(ParameterType.BOOLEAN)
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    .name("DisableMultiRegionAccessPoints")
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    .builtIn("AWS::S3::DisableMultiRegionAccessPoints")
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    .required(true)
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    .defaultValue(Value.booleanValue(false))
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    .documentation("Whether multi-region access points (MRAP) should be disabled.")
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    .build();
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```
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#### S3 Force Path Style Parameter
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```java { .api }
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/**
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 * S3-specific parameter for path-style endpoints. MUST only be used by S3 rules.
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 */
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public static final Parameter S3_FORCE_PATH_STYLE = Parameter.builder()
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    .type(ParameterType.BOOLEAN)
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    .name("ForcePathStyle")
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    .builtIn("AWS::S3::ForcePathStyle")
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    .documentation("When true, force a path-style endpoint to be used where the bucket name is part of the path.")
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    .build();
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```
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#### S3 Use ARN Region Parameter
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```java { .api }
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/**
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 * S3-specific parameter for ARN region usage. MUST only be used by S3 rules.
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 */
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public static final Parameter S3_USE_ARN_REGION = Parameter.builder()
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    .type(ParameterType.BOOLEAN)
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    .name("UseArnRegion")
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    .builtIn("AWS::S3::UseArnRegion")
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    .documentation("When an Access Point ARN is provided and this flag is enabled, the SDK MUST use the ARN's region when constructing the endpoint instead of the client's configured region.")
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    .build();
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```
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#### S3 Use Global Endpoint Parameter
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```java { .api }
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/**
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 * S3-specific parameter for global endpoint usage. MUST only be used by S3 rules.
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 */
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public static final Parameter S3_USE_GLOBAL_ENDPOINT = Parameter.builder()
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    .type(ParameterType.BOOLEAN)
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    .name("UseGlobalEndpoint")
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    .builtIn("AWS::S3::UseGlobalEndpoint")
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    .required(true)
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    .defaultValue(Value.booleanValue(false))
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    .documentation("Whether the global endpoint should be used, rather then the regional endpoint for us-east-1.")
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    .build();
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```
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### S3 Control Parameters
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#### S3 Control Use ARN Region Parameter
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```java { .api }
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/**
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 * S3Control-specific parameter for ARN region usage. MUST only be used by S3Control rules.
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 */
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public static final Parameter S3_CONTROL_USE_ARN_REGION = Parameter.builder()
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    .type(ParameterType.BOOLEAN)
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    .name("UseArnRegion")
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    .builtIn("AWS::S3Control::UseArnRegion")
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    .documentation("When an Access Point ARN is provided and this flag is enabled, the SDK MUST use the ARN's region when constructing the endpoint instead of the client's configured region.")
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    .build();
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```
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### STS Parameters
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#### STS Use Global Endpoint Parameter
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```java { .api }
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/**
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 * STS-specific parameter for global endpoint usage. MUST only be used by STS rules.
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 */
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public static final Parameter STS_USE_GLOBAL_ENDPOINT = Parameter.builder()
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    .type(ParameterType.BOOLEAN)
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    .name("UseGlobalEndpoint")
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    .builtIn("AWS::STS::UseGlobalEndpoint")
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    .required(true)
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    .defaultValue(Value.booleanValue(false))
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    .documentation("Whether the global endpoint should be used, rather then the regional endpoint for us-east-1.")
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    .build();
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```
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**Usage Examples:**
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```java
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import software.amazon.smithy.rulesengine.language.syntax.parameters.Parameter;
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import software.amazon.smithy.rulesengine.aws.language.functions.AwsBuiltIns;
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// Access AWS built-in parameters
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Parameter regionParam = AwsBuiltIns.REGION;
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Parameter dualStackParam = AwsBuiltIns.DUALSTACK;
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Parameter fipsParam = AwsBuiltIns.FIPS;
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// These parameters are automatically available in endpoint rules
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// when using the AwsRuleSetExtension
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// Example parameter usage in rule expressions:
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// - Built-in name: "AWS::Region" 
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// - Parameter name: "Region"
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// - Type: STRING
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// - Required: varies by parameter
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```
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## Parameter Categories
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### Universal AWS Parameters
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- `REGION` - AWS region for request routing
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- `DUALSTACK` - Enable IPv4/IPv6 dual-stack endpoints  
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- `FIPS` - Require FIPS-compliant endpoints
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### Authentication Parameters
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- `ACCOUNT_ID` - AWS account identifier
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- `ACCOUNT_ID_ENDPOINT_MODE` - Account-specific endpoint mode
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- `CREDENTIAL_SCOPE` - Credential scoping information
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### Service-Specific Parameters
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- **S3**: Accelerate, MRAP, path-style, ARN region, global endpoint
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- **S3 Control**: ARN region usage
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- **STS**: Global endpoint preference
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All parameters include comprehensive documentation strings explaining their purpose and usage constraints.