Use CreateGrant with an Amazon SDK or CLI

        public static async Task Main()
        {
            var client = new AmazonKeyManagementServiceClient();

            // The identity that is given permission to perform the operations
            // specified in the grant.
            var grantee = "arn:aws:iam::111122223333:role/ExampleRole";

            // The identifier of the AWS KMS key to which the grant applies. You
            // can use the key ID or the Amazon Resource Name (ARN) of the KMS key.
            var keyId = "7c9eccc2-38cb-4c4f-9db3-766ee8dd3ad4";

            var request = new CreateGrantRequest
            {
                GranteePrincipal = grantee,
                KeyId = keyId,

                // A list of operations that the grant allows.
                Operations = new List<string>
                {
                    "Encrypt",
                    "Decrypt",
                },
            };

            var response = await client.CreateGrantAsync(request);

            string grantId = response.GrantId; // The unique identifier of the grant.
            string grantToken = response.GrantToken; // The grant token.

            Console.WriteLine($"Id: {grantId}, Token: {grantToken}");
        }
    }

To create a grant

The following create-grant example creates a grant that allows the exampleUser user to use the decrypt command on the 1234abcd-12ab-34cd-56ef-1234567890ab example KMS key. The retiring principal is the adminRole role. The grant uses the EncryptionContextSubset grant constraint to allow this permission only when the encryption context in the decrypt request includes the "Department": "IT" key-value pair.

aws kms create-grant \
    --key-id 1234abcd-12ab-34cd-56ef-1234567890ab \
    --grantee-principal arn:aws:iam::123456789012:user/exampleUser \
    --operations Decrypt \
    --constraints EncryptionContextSubset={Department=IT} \
    --retiring-principal arn:aws:iam::123456789012:role/adminRole

Output:

{
    "GrantId": "1a2b3c4d2f5e69f440bae30eaec9570bb1fb7358824f9ddfa1aa5a0dab1a59b2",
    "GrantToken": "<grant token here>"
}

To view detailed information about the grant, use the list-grants command.

For more information, see Grants in Amazon KMS in the Amazon Key Management Service Developer Guide.

    /**
     * Grants permissions to a specified principal on a customer master key (CMK) asynchronously.
     *
     * @param keyId             The unique identifier for the customer master key (CMK) that the grant applies to.
     * @param granteePrincipal  The principal that is given permission to perform the operations that the grant permits on the CMK.
     * @return A {@link CompletableFuture} that, when completed, contains the ID of the created grant.
     * @throws RuntimeException If an error occurs during the grant creation process.
     */
    public CompletableFuture<String> grantKeyAsync(String keyId, String granteePrincipal) {
        List<GrantOperation> grantPermissions = List.of(
            GrantOperation.ENCRYPT,
            GrantOperation.DECRYPT,
            GrantOperation.DESCRIBE_KEY
        );

        CreateGrantRequest grantRequest = CreateGrantRequest.builder()
            .keyId(keyId)
            .name("grant1")
            .granteePrincipal(granteePrincipal)
            .operations(grantPermissions)
            .build();

        CompletableFuture<CreateGrantResponse> responseFuture = getAsyncClient().createGrant(grantRequest);
        responseFuture.whenComplete((response, ex) -> {
            if (ex == null) {
                logger.info("Grant created successfully with ID: " + response.grantId());
            } else {
                if (ex instanceof KmsException kmsEx) {
                    throw new RuntimeException("Failed to create grant: " + kmsEx.getMessage(), kmsEx);
                } else {
                    throw new RuntimeException("An unexpected error occurred: " + ex.getMessage(), ex);
                }
            }
        });

        return responseFuture.thenApply(CreateGrantResponse::grantId);
    }

suspend fun createNewGrant(
    keyIdVal: String?,
    granteePrincipalVal: String?,
    operation: String,
): String? {
    val operationOb = GrantOperation.fromValue(operation)
    val grantOperationList = ArrayList<GrantOperation>()
    grantOperationList.add(operationOb)

    val request =
        CreateGrantRequest {
            keyId = keyIdVal
            granteePrincipal = granteePrincipalVal
            operations = grantOperationList
        }

    KmsClient { region = "us-west-2" }.use { kmsClient ->
        val response = kmsClient.createGrant(request)
        return response.grantId
    }
}

class GrantManager:
    def __init__(self, kms_client):
        self.kms_client = kms_client


    def create_grant(self, key_id):
        """
        Creates a grant for a key that lets a principal generate a symmetric data
        encryption key.

        :param key_id: The ARN or ID of the key.
        :return: The grant that is created.
        """
        principal = input(
            f"Enter the ARN of a principal, such as an IAM role, to grant that role "
            f"GenerateDataKey permissions on key {key_id}: "
        )
        if principal != "":
            try:
                grant = self.kms_client.create_grant(
                    KeyId=key_id,
                    GranteePrincipal=principal,
                    Operations=["GenerateDataKey"],
                )
            except ClientError as err:
                logger.error(
                    "Couldn't create a grant on key %s. Here's why: %s",
                    key_id,
                    err.response["Error"]["Message"],
                )
            else:
                print(f"Grant created on key {key_id}.")
                return grant
        else:
            print("Skipping grant creation.")