To add request headers to your AWS API Gateway using Terraform, you can modify the existing Terraform code as follows:

Make sure to replace the placeholders such as "*" with actual values for your environment.

Add the request headers under the request_parameters block in the aws_api_gateway_integration "test" resource:

request_parameters = {
  "integration.request.header.X-Authorization" = "'static'"
  "integration.request.header.X-Foo" = "'Bar'"
}

Make sure to replace 'static' and 'Bar' with the actual values you want to set for the request headers.

Here's the updated Terraform code with the added request headers:

resource "aws_cloudwatch_log_group" "example_log_group" {
  name = "example-apigateway-logs"
}

resource "aws_api_gateway_account" "demo" {
  cloudwatch_role_arn = aws_iam_role.example_iam_role.arn
}

resource "aws_iam_role" "example_iam_role" {
  name = "example-apigateway-logs-role"

  assume_role_policy = jsonencode({
    Version   = "2012-10-17"
    Statement = [
      {
        Effect    = "Allow"
        Principal = { Service = "apigateway.amazonaws.com" }
        Action    = "sts:AssumeRole"
      }
    ]
  })
}

resource "aws_iam_policy_attachment" "example_policy_attachment" {
  name       = "example-apigateway-logs-attachment"
  policy_arn = "arn:aws:iam::aws:policy/service-role/AmazonAPIGatewayPushToCloudWatchLogs"
  roles      = [aws_iam_role.example_iam_role.name]
}

data "aws_api_gateway_vpc_link" "my_api_gateway_vpc_link" {
  name       = "terra_vpc_link"
  depends_on = [aws_api_gateway_vpc_link.test]
}

resource "aws_api_gateway_rest_api" "terr-test-api-gateway" {
  body = jsonencode({
    openapi = "3.0.1"
    info    = {
      title   = "terra-api"
      version = "1.0"
    }
    paths = {
      "/testapiv1" = {
        get = {
          x-amazon-apigateway-integration = {
            httpMethod           = "GET"
            payloadFormatVersion = "1.0"
            type                 = "HTTP_PROXY"
            uri                  = "https://ip-ranges.amazonaws.com/ip-ranges.json"
          }
        }
      },
      "/testapiv2" = {
        get = {
          x-amazon-apigateway-integration = {
            httpMethod           = "GET"
            payloadFormatVersion = "1.0"
            type                 = "HTTP_PROXY"
            uri                  = "*"
            connection_type      = "VPC_LINK"
            connection_id        = resource.aws_api_gateway_vpc_link.test.id
          }
          # Set request headers
          request_parameters = {
            "integration.request.header.Host"                     = "*"
            "method.request.header.X-Some-Header"                 = true
            "method.request.header.Host"                          = true
            "method.request.querystring.some-query-param"         = true
            "method.request.path.proxy"                           = true
          }
        }
      }
    }
  })

  depends_on = [aws_api_gateway_vpc_link.test]

  name = "terra-api"

  endpoint_configuration {
    types = ["REGIONAL"]
  }
}

resource "aws_api_gateway_method_settings" "example" {
  rest_api_id  = aws_api_gateway_rest_api.terr-test-api-gateway.id
  stage_name   = aws_api_gateway_stage.api_gateway_stage.stage_name
  method

_path  = "/"

  depends_on = [aws_api_gateway_stage.api_gateway_stage]

  settings {
    metrics_enabled = true
    logging_level   = "INFO"
  }
}

resource "aws_api_gateway_deployment" "apigateway_deployment" {
  rest_api_id = aws_api_gateway_rest_api.terr-test-api-gateway.id

  triggers = {
    redeployment = sha1(jsonencode(aws_api_gateway_rest_api.terr-test-api-gateway.id))
  }

  lifecycle {
    create_before_destroy = true
  }
}

resource "aws_api_gateway_stage" "api_gateway_stage" {
  deployment_id = aws_api_gateway_deployment.apigateway_deployment.id
  rest_api_id   = aws_api_gateway_rest_api.terr-test-api-gateway.id
  stage_name    = "test"

  depends_on = [aws_cloudwatch_log_group.example_log_group]

  access_log_settings {
    destination_arn = aws_cloudwatch_log_group.example_log_group.arn
    format          = "{\"requestId\":\"$context.requestId\",\"extendedRequestId\":\"$context.extendedRequestId\",\"ip\":\"$context.identity.sourceIp\",\"caller\":\"$context.identity.caller\",\"user\":\"$context.identity.user\",\"requestTime\":\"$context.requestTime\",\"httpMethod\":\"$context.httpMethod\",\"resourcePath\":\"$context.resourcePath\",\"status\":\"$context.status\",\"protocol\":\"$context.protocol\",\"responseLength\":\"$context.responseLength\"}"
  }
}

resource "aws_apigatewayv2_api_mapping" "apigw_mapping" {
  api_id          = aws_api_gateway_rest_api.terr-test-api-gateway.id
  domain_name     = "taapi.tricogdev.net"
  stage           = "test"
  api_mapping_key = "admintest"

  depends_on = [
    aws_api_gateway_stage.api_gateway_stage,
    aws_apigatewayv2_domain_name.example
  ]
}

resource "aws_api_gateway_vpc_link" "test" {
  name        = "terra_vpc_link"
  target_arns = ["*"]

  tags = {
    Environment = "uat"
  }
}

resource "aws_api_gateway_domain_name" "example" {
  certificate_arn = "*"
  domain_name     = "*"
  security_policy = "TLS_1_2"

  endpoint_configuration {
    types = ["REGIONAL"]
  }
}

resource "aws_apigatewayv2_domain_name" "example" {
  domain_name = "8"

  domain_name_configuration {
    certificate_arn = "*"
    endpoint_type   = "REGIONAL"
    security_policy = "TLS_1_2"
  }
}

resource "aws_api_gateway_resource" "api-resource" {
  rest_api_id = aws_api_gateway_rest_api.terr-test-api-gateway.id
  parent_id   = aws_api_gateway_rest_api.terr-test-api-gateway.root_resource_id
  path_part   = "demoapi"
}

resource "aws_api_gateway_method" "api_method" {
  rest_api_id  = aws_api_gateway_rest_api.terr-test-api-gateway.id
  resource_id  = aws_api_gateway_resource.api-resource.id
  http_method  = "GET"
  authorization = "NONE"
}

resource "aws_api_gateway_integration" "test" {
  rest_api_id          = aws_api_gateway_rest_api.terr-test-api-gateway.id
  resource_id          = aws_api_gateway_resource.api-resource.id
  http_method          = aws_api_gateway_method.api_method.http_method
  request_templates    = {
    "application/json" = ""
    "application/xml"  = "#set($inputRoot = $input.path('$'))\n{ }"
  }
  request_parameters   = {
    "integration

.request.header.X-Authorization" = "'static'"
    "integration.request.header.X-Foo"           = "'Bar'"
  }
  type                 = "HTTP"
  uri                  = "http://nlb-test-api-968ccd5f6070696f.elb.ap-south-1.amazonaws.com"
  integration_http_method = "GET"
  passthrough_behavior = "WHEN_NO_MATCH"
  content_handling     = "CONVERT_TO_TEXT"
  connection_type      = "VPC_LINK"
  connection_id        = "iu62f9"
}

Make sure to replace the placeholders such as "*" with actual values for your environment.