CreateAuthenticatedSessionToken: The signature of the request does not match the request parameters

Question

I'm creating an app using the SODA Architecture. 
I could successfully create an app and make the client to authorize it. 
Result of newApplicationCreationInfo:
<?xml version="1.0" encoding="UTF-8"?>
<response>
<status>
<code>0</code>
</status>
<wc:info xmlns:wc="urn:com.microsoft.wc.methods.response.NewApplicationCreationInfo">
<app-id>4417587e-46d1-49ee-a0fa-50dbfdcf932c</app-id>
<shared-secret>gBksYDAqcuAUXK+zyvfFW9F0sy8nchwnplJ6K7aKmAM=</shared-secret>
<app-token>AiAAANDl....A5b9fxVIlXEloouci6jGhY/A==</app-token>
</wc:info>
</response>
I'm using the app-token to build the redirect url, and I get to authorize the new app. 
then, using the new child app id and the shared-secret I built the 
CreateAuthenticatedSessionToken:
<?xml version="1.0" encoding="UTF-8"?>
<wc-request:request xmlns:wc-request="urn:com.microsoft.wc.request">
<header>
<method>CreateAuthenticatedSessionToken</method>
<method-version>2</method-version>
<app-id>4417587e-46d1-49ee-a0fa-50dbfdcf932c</app-id>
<language>en</language>
<country>US</country>
<msg-time>2013-01-01T00:00:00Z</msg-time>
<msg-ttl>1800</msg-ttl>
<version>2.0.0.0</version>
</header>
<info>
<auth-info>
<app-id>4417587e-46d1-49ee-a0fa-50dbfdcf932c</app-id>
<credential>
<appserver2>
<hmacSig algName="HMACSHA256">PcW4f9krD1O43O4JGBGEkqDlpatFIUUQY9JejHji0XA=</hmacSig>
<content>
<app-id>4417587e-46d1-49ee-a0fa-50dbfdcf932c</app-id>
<hmac>HMACSHA256</hmac>
<signing-time>2013-12-17T14:19:58.623Z</signing-time>
</content>
</appserver2>
</credential>
</auth-info>
</info>
</wc-request:request>
Being hmacSig value the encryption of "<content>....</content>" using shared-secret value as private key:
hmacSig = Encodingutil.base64Encode(Crypto.generateMac('hmacSHA256', Blob.valueOf(body), Blob.valueOf(sharedSecret)))
this returns an error code 11: The signature of the request does not match the request parameters.
I'm using the following endpoint: https://platform.healthvault-ppe.com/platform/wildcat.ashx
Also the redirection url I received after authorizing the app contains the following: 
https://<MY_URL>/?gws_rd=cr&ei=h5ewUuKLJa7IsASc4YHIAw I'm not using this parameters, if that helps.
Any hint will be greatly appreciated.
UPDATE: I already checked the HMAC encoding using a third party service and it returned the same as my app

Answer 1

I figured this out (God bless Pair Programming):
I was signing incorrectly: 
On the newApplicationCreationInfo:
My Shared Secret is : gBksYDAqcuAUXK+zyvfFW9F0sy8nchwnplJ6K7aKmAM=
But BEFORE hashing the "<content>...</content>" i need to decode my secret that is:
hmacsig = calculateHMAC256(content, sharedSecret.decodeBase64())