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# Environment Credential
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Authenticates using environment variables for service principal credentials, supporting both client secret and client certificate authentication.
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## Capabilities
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### Environment Variable Authentication
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Reads credential information from environment variables to authenticate service principals.
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```java { .api }
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/**
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 * Authenticates using environment variables for service principal credentials
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 */
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class EnvironmentCredential implements TokenCredential {
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    Mono<AccessToken> getToken(TokenRequestContext request);
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    AccessToken getTokenSync(TokenRequestContext request);
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}
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class EnvironmentCredentialBuilder extends CredentialBuilderBase<EnvironmentCredentialBuilder> {
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    EnvironmentCredentialBuilder authorityHost(String authorityHost);
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    EnvironmentCredentialBuilder executorService(ExecutorService executorService);
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    EnvironmentCredential build();
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}
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```
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**Supported Environment Variables:**
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**For Client Secret Authentication:**
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- `AZURE_CLIENT_ID` - The application (client) ID
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- `AZURE_CLIENT_SECRET` - The client secret
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- `AZURE_TENANT_ID` - The tenant ID
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- `AZURE_AUTHORITY_HOST` (optional) - The authority host URL
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**For Client Certificate Authentication:**
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- `AZURE_CLIENT_ID` - The application (client) ID
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- `AZURE_CLIENT_CERTIFICATE_PATH` - Path to PEM or PFX certificate file
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- `AZURE_CLIENT_CERTIFICATE_PASSWORD` - Certificate password (if required)
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- `AZURE_TENANT_ID` - The tenant ID
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- `AZURE_AUTHORITY_HOST` (optional) - The authority host URL
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**Usage Examples:**
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```java
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import com.azure.identity.EnvironmentCredential;
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import com.azure.identity.EnvironmentCredentialBuilder;
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// Create credential using environment variables
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TokenCredential credential = new EnvironmentCredentialBuilder()
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    .build();
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// Use with Azure SDK clients
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SecretClient client = new SecretClientBuilder()
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    .vaultUrl("https://myvault.vault.azure.net/")
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    .credential(credential)
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    .buildClient();
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```
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## Exception Handling
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Throws `CredentialUnavailableException` when required environment variables are not set or invalid.