Oauth 2.0 access token issue - mule

Question

I am consuming one of the Google API's and provided all the OAuth 2.0 credentials in HTTP requester.I need to generate the access token, capture the token and pass this access token in the headers to get the output.But I am getting the error:
Execution of the expression "'Bearer' + payload.access_token" failed.
(org.mule.api.expression.ExpressionRuntimeException).
Is this the correct way of generating the token and accessing it?
<?xml version="1.0" encoding="UTF-8"?>
<mule xmlns:oauth2="http://www.mulesoft.org/schema/mule/oauth2" xmlns:http="http://www.mulesoft.org/schema/mule/http" xmlns="http://www.mulesoft.org/schema/mule/core" xmlns:doc="http://www.mulesoft.org/schema/mule/documentation"
xmlns:spring="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-current.xsd
http://www.mulesoft.org/schema/mule/core http://www.mulesoft.org/schema/mule/core/current/mule.xsd
http://www.mulesoft.org/schema/mule/http http://www.mulesoft.org/schema/mule/http/current/mule-http.xsd
http://www.mulesoft.org/schema/mule/oauth2 http://www.mulesoft.org/schema/mule/oauth2/current/mule-oauth2.xsd">
<http:listener-config name="HTTP_Listener_Configuration" host="0.0.0.0" port="8081" doc:name="HTTP Listener Configuration"/>
<http:request-config name="HTTP_Request_Configuration" protocol="HTTPS" host="www.googleapis.com" port="443" doc:name="HTTP Request Configuration">
<oauth2:authorization-code-grant-type clientId="client_id" clientSecret="client_secret" redirectionUrl="http://localhost:8082/callback">
<oauth2:authorization-request authorizationUrl="https://accounts.google.com/o/oauth2/auth" localAuthorizationUrl="http://localhost:8082/login" scopes="https://www.googleapis.com/auth/admin.directory.user"/>
<oauth2:token-request tokenUrl="https://accounts.google.com/o/oauth2/token">
<oauth2:token-response accessToken="#[payload.access_token]"/>
</oauth2:token-request>
</oauth2:authorization-code-grant-type>
</http:request-config>
<flow name="csdfFlow">
<http:listener config-ref="HTTP_Listener_Configuration" path="/test" doc:name="HTTP"/>
<http:request config-ref="HTTP_Request_Configuration" path="/admin/directory/v1/users?domain=aabbcc.com" method="GET" doc:name="HTTP">
<http:request-builder>
<http:header headerName="Authorization" value="#['Bearer '+payload.access_token]"/>
</http:request-builder>
<http:success-status-code-validator values="0..599"/>
</http:request>
<logger message="#[payload]" level="INFO" doc:name="Logger"/>
</flow>
</mule>

Answer 1

The expression seems to be wrong.
Try value="Bearer #[payload.access_token]"

Answer 2

you can pass Bearer token in header as shown below : Try like this:

Answer 3

try this it may help you:
<http:header headerName="Authorization" value="Bearer
#[flowVars.accesstoken]"/>