Unexpected response code 400

**Issue by [g123k](https://github.com/g123k)**
_Friday Jun 05, 2015 at 12:58 GMT_
_Originally opened as https://github.com/googlesamples/android-credentials/issues/3_

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When I try to save the credentials for the first time, I have this message in the logcat:

```
E/Volley ( 1070): [250] BasicNetwork.performRequest: Unexpected response code 400 for https://www.googleapis.com/credentials/v1/credentials?alt=proto&header.playServicesVersion=7571000&obfuscationKey=44838BE022CB8E787432945F2B755C422766B72D16B5DDB5CBD56C525143C8AE
E/CredentialsApi( 1309): Error when saving credential.
E/CredentialsApi( 1309): com.google.android.gms.auth.api.credentials.a: java.io.IOException: Server error.
E/CredentialsApi( 1309): at com.google.android.gms.auth.api.credentials.d.a(SourceFile:329)
E/CredentialsApi( 1309): at com.google.android.gms.auth.api.credentials.be.b.e.a(SourceFile:181)
E/CredentialsApi( 1309): at com.google.android.gms.auth.api.credentials.be.b.e.a(SourceFile:33)
E/CredentialsApi( 1309): at com.google.android.gms.common.service.g.run(SourceFile:178)
E/CredentialsApi( 1309): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
E/CredentialsApi( 1309): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
E/CredentialsApi( 1309): at java.lang.Thread.run(Thread.java:818)
E/CredentialsApi( 1309): Caused by: java.io.IOException: Server error.
E/CredentialsApi( 1309): at com.google.android.gms.auth.api.credentials.be.c.d.a(SourceFile:124)
E/CredentialsApi( 1309): at com.google.android.gms.auth.api.credentials.be.s.a(SourceFile:95)
E/CredentialsApi( 1309): at com.google.android.gms.auth.api.credentials.be.d.a(SourceFile:279)
E/CredentialsApi( 1309): at com.google.android.gms.auth.api.credentials.be.d.a(SourceFile:92)
E/CredentialsApi( 1309): at com.google.android.gms.auth.api.credentials.be.z.onTransact(SourceFile:135)
E/CredentialsApi( 1309): at android.os.Binder.execTransact(Binder.java:446)
E/CredentialsApi( 1309): Caused by: com.google.android.gms.auth.api.credentials.be.a.c
E/CredentialsApi( 1309): at com.google.android.gms.auth.api.credentials.be.a.b.a(SourceFile:469)
E/CredentialsApi( 1309): at com.google.android.gms.auth.api.credentials.be.a.b.a(SourceFile:156)
E/CredentialsApi( 1309): at com.google.android.gms.auth.api.credentials.be.c.d.a(SourceFile:117)
E/CredentialsApi( 1309): ... 5 more
```

I don't think the error is on the client-side, but the Intent in the onActivityResult is empty.

Start by reproducing the first credential-save flow and inspect the onActivityResult callback alongside the Logcat response from the credentials API. Determine whether the empty Intent is produced by the sample or the service; done means the cause is identified and the flow no longer returns the unexpected 400 error.

Written by the indexing model from the issue text.